Although I do think that Ash would use his Sinnoh team against Paul in the future, I always wonder which of Ash's old pokemon would put up an awesome fight against Paul's team. So taking Paul's main team that he used against Ash on the 6 vs. 6 battle and taking 6 of Ash's old pokemon...here's what I was thinking:
Pikachu vs. Honchkrow
Obviously an advantage for Pikachu. Most of Honchkrow's moves are pretty straightforward. Night Slash and Sky Attack are physical attacks that Pikachu can either dodge or combat with Iron Tail. And iirc, it knows Shadow Ball and Dark Pulse as well which again, Pikachu can handle. Then we have Pikachu's Thunderbolt and Volt Tackle that can knock Honchkrow out. Honchkrow's strong but Pikachu, especially at its best, is stronger imo.
Charizard vs. Torterra
Type wise, Charizard has an advantage. It just needs to worry about Stone Edge. However we've seen it face many opponents before and Charizard's experience, training, and strength would for sure overcome one attack from Torterra. Charizard also has a pleathora of attacks that it could use against Torterra so Ash could definitely use Charizard's many attacks for some awesome combinations to win against Torterra. There's the fact that Charizard as an aerial battler and so Torterra is going to have a hard time trying to keep up with Charizard since it's so stagnant while Charizard is up in the air. Charizard is definitely Ash's pokemon to use against Paul if Ash were to use old pokemon.
Donphan vs. Electabuzz
Electabuzz is seen as one of Paul's strongest but yet, it's probably no match for Ash's Donphan. Its electric attacks won't have much affect against Donphan and Donphan's got the defense the handle its Brick Break. Light Screen is known for throwing Ash off guard but it only protects Paul's pokemon from special attacks and other than Hidden Power and Hyper Beam, Donphan's attacks are physical. And Electabuzz can't use Protect too much either. And while Donphan doesn't have a ground move, it has hard hitting moves and strength that can overcome Electabuzz. Not to mention, if the writers weren't so paranoid about Earthquake, Donphan could definitely be the pokemon able to take down Electabuzz.
Snorlax vs. Ursaring
Both pokemon have shown to take a lot of hits before falling, both are normal types, but Snorlax could win against Ursaring for sure. Sure Ursaring has fighting moves but Snorlax faced both of Greta's fighting type pokemon and beat them. Snorlax has great defences, knowing Protect and being able to use Rest. At the same time, it's pretty strong with Ice Punch, Body Slam, Headbutt, etc. Ursaring would have a hard time taking Snorlax down.
Sceptile vs. Weavile
Leaf Blade vs. Metal Claw basically. While Weavile has ice moves that could hurt Sceptile, Sceptile has proven that it has a fighter's spirit and I'm sure it won't go down that easily against Weavile's ice attacks. Then there's the physical combat where I think Sceptile dominates. With Leaf Blade and Slam, Weavile is not going to fare well against Sceptile's toughness. Sceptile also has some strong special moves as well that could throw Weavile off guard. Finally, Weavile is probably Paul's weakest pokemon, Sceptile wouldn't go down easily from it.
Swellow vs. Magmortar
Swellow would actually benefit from being burned by Magmortar. Swellow definitely has the guts to overcome its weaknesses and because of its ability, Magmortar's burn would only make Swellow. If Swellow would learn Facade, the combination would be pretty powerful. And although Magmortar has Rock Tomb, iirc it only produces rocks on the ground so Swellow shouldn't worry about that since it's an aerial battler. If Rock Tomb were to strike in the air, Swellow does have its speed and Double Team to get out of trouble. What Swellow has is speed, coupled with guts and strength too. It's a contender against Paul and can use its ability to its full potential against Magmortar. And while it's true that Swellow can't stay in a battle for too long with a burn condition, we know that it doesn't go down easily at all and it definitely has the stamina to hold it out.
The 6 vs. 6 battle against Paul showed a couple of things that definitely led to Ash's downfall besides Paul's pokemon's strength. Ash had pokemon who were inflicted with status conditions. Electabuzz's electric moves and Magmortar's Flame Body. However, if Ash uses Donphan and Swellow respectively, these status conditions wouldn't occur (or for Swellow's case would actually benefit it to an extent). Then there's Ursaring's guts which if Ursaring is faced against a pokemon that can also take a lot of damage such as Snorlax, it wouldn't be able to win as easily as it did before. Light Screen can definitely be combated by physical moves which Swellow, Sceptile, Donphan, and Snorlax excel at. And considering that Charizard's ace move is usually Seismic Toss, Light Screen won't be a big problem. Finally, Paul's switching was a problem. Ash has to pair pokemon up to face Paul and switch back. If this battle were to occur,
Pikachu, as well as all of Ash's other pokemon can probably handle Weavile.
Charizard can also handle Ursaring, Honchkrow, and Magmortar.
Sceptile can probably handle Ursaring, Electabuzz, and Torterra.
Donphan can probably take Ursaring, Honchkrow, and Magmortar.
Swellow can actually go up against Electabuzz, Ursaring, Torterra and Honchkrow.
Snorlax can go up against Electabuzz, Honchkrow, Magmortar, and Torterra as well.
So to me, Pikachu, Charizard, Sceptile, Donphan, Swellow, and Snorlax are probably pokemon that are suited to go against Paul and win.
However, this battle is pretty much fantasy at this point lol. I mean imo, while this battle would be cool, Ash is most likely going to use his Sinnoh team to face Paul for storyline purposes. But hey, it's fun thinking about it.
Pikachu vs. Honchkrow
Obviously an advantage for Pikachu. Most of Honchkrow's moves are pretty straightforward. Night Slash and Sky Attack are physical attacks that Pikachu can either dodge or combat with Iron Tail. And iirc, it knows Shadow Ball and Dark Pulse as well which again, Pikachu can handle. Then we have Pikachu's Thunderbolt and Volt Tackle that can knock Honchkrow out. Honchkrow's strong but Pikachu, especially at its best, is stronger imo.
Charizard vs. Torterra
Type wise, Charizard has an advantage. It just needs to worry about Stone Edge. However we've seen it face many opponents before and Charizard's experience, training, and strength would for sure overcome one attack from Torterra. Charizard also has a pleathora of attacks that it could use against Torterra so Ash could definitely use Charizard's many attacks for some awesome combinations to win against Torterra. There's the fact that Charizard as an aerial battler and so Torterra is going to have a hard time trying to keep up with Charizard since it's so stagnant while Charizard is up in the air. Charizard is definitely Ash's pokemon to use against Paul if Ash were to use old pokemon.
Donphan vs. Electabuzz
Electabuzz is seen as one of Paul's strongest but yet, it's probably no match for Ash's Donphan. Its electric attacks won't have much affect against Donphan and Donphan's got the defense the handle its Brick Break. Light Screen is known for throwing Ash off guard but it only protects Paul's pokemon from special attacks and other than Hidden Power and Hyper Beam, Donphan's attacks are physical. And Electabuzz can't use Protect too much either. And while Donphan doesn't have a ground move, it has hard hitting moves and strength that can overcome Electabuzz. Not to mention, if the writers weren't so paranoid about Earthquake, Donphan could definitely be the pokemon able to take down Electabuzz.
Snorlax vs. Ursaring
Both pokemon have shown to take a lot of hits before falling, both are normal types, but Snorlax could win against Ursaring for sure. Sure Ursaring has fighting moves but Snorlax faced both of Greta's fighting type pokemon and beat them. Snorlax has great defences, knowing Protect and being able to use Rest. At the same time, it's pretty strong with Ice Punch, Body Slam, Headbutt, etc. Ursaring would have a hard time taking Snorlax down.
Sceptile vs. Weavile
Leaf Blade vs. Metal Claw basically. While Weavile has ice moves that could hurt Sceptile, Sceptile has proven that it has a fighter's spirit and I'm sure it won't go down that easily against Weavile's ice attacks. Then there's the physical combat where I think Sceptile dominates. With Leaf Blade and Slam, Weavile is not going to fare well against Sceptile's toughness. Sceptile also has some strong special moves as well that could throw Weavile off guard. Finally, Weavile is probably Paul's weakest pokemon, Sceptile wouldn't go down easily from it.
Swellow vs. Magmortar
Swellow would actually benefit from being burned by Magmortar. Swellow definitely has the guts to overcome its weaknesses and because of its ability, Magmortar's burn would only make Swellow. If Swellow would learn Facade, the combination would be pretty powerful. And although Magmortar has Rock Tomb, iirc it only produces rocks on the ground so Swellow shouldn't worry about that since it's an aerial battler. If Rock Tomb were to strike in the air, Swellow does have its speed and Double Team to get out of trouble. What Swellow has is speed, coupled with guts and strength too. It's a contender against Paul and can use its ability to its full potential against Magmortar. And while it's true that Swellow can't stay in a battle for too long with a burn condition, we know that it doesn't go down easily at all and it definitely has the stamina to hold it out.
The 6 vs. 6 battle against Paul showed a couple of things that definitely led to Ash's downfall besides Paul's pokemon's strength. Ash had pokemon who were inflicted with status conditions. Electabuzz's electric moves and Magmortar's Flame Body. However, if Ash uses Donphan and Swellow respectively, these status conditions wouldn't occur (or for Swellow's case would actually benefit it to an extent). Then there's Ursaring's guts which if Ursaring is faced against a pokemon that can also take a lot of damage such as Snorlax, it wouldn't be able to win as easily as it did before. Light Screen can definitely be combated by physical moves which Swellow, Sceptile, Donphan, and Snorlax excel at. And considering that Charizard's ace move is usually Seismic Toss, Light Screen won't be a big problem. Finally, Paul's switching was a problem. Ash has to pair pokemon up to face Paul and switch back. If this battle were to occur,
Pikachu, as well as all of Ash's other pokemon can probably handle Weavile.
Charizard can also handle Ursaring, Honchkrow, and Magmortar.
Sceptile can probably handle Ursaring, Electabuzz, and Torterra.
Donphan can probably take Ursaring, Honchkrow, and Magmortar.
Swellow can actually go up against Electabuzz, Ursaring, Torterra and Honchkrow.
Snorlax can go up against Electabuzz, Honchkrow, Magmortar, and Torterra as well.
So to me, Pikachu, Charizard, Sceptile, Donphan, Swellow, and Snorlax are probably pokemon that are suited to go against Paul and win.
However, this battle is pretty much fantasy at this point lol. I mean imo, while this battle would be cool, Ash is most likely going to use his Sinnoh team to face Paul for storyline purposes. But hey, it's fun thinking about it.