I think Ash's Sinnoh Team should be the ones able to face Paul. No reserves, either the ones from the opening or any that weren't in the opening. Just the Sinnoh pokemon and Pikachu. Now whether or not the sixth member is Gible or Gliscor is a whole different story but I do think that Ash's pokemon that he had throughout Sinnoh should be the pokemon he should use against Paul.
I understand that it's more logical if Ash would use his reserves. I mean Charizard is a great pokemon that always comes through for Ash. Sceptile and Swellow have certainly shown a lot of their awesomeness during AG. Snorlax is a powerhouse, Glalie never "lost" a match in a league yet, and Donphan helped out in the BF beating Lucy's signature pokemon and its typing, attacks, and defenses would be perfect against Paul's Electabuzz (a pokemon that seems to be considered one of his signature pokemon). A team with them and Paul could be beaten pretty easily.
However, story wise, the team that should battle Paul should be Ash's Sinnoh team. The battle in the Sinnoh league will prove which style of training is better. Paul's style is to get the strongest of the strongest and to rotate his pokemon in order to get the best advantage. Ash's is to work with his pokemon and train with them no matter what kind of pokemon they are. If Ash uses his reserves against Paul, he wouldn't be proving anything. Ash can use as many reserves for other matches but I think the one vs. Paul should be all Sinnoh and Pikachu. Besides, it's more dramatic if it's the Sinnoh team vs. Paul.
These are the pokemon that have been with Ash thoughout the whole Sinnoh region. And what better way to show how far they have come than a battle with Ash's main rival in the Sinnoh region: Paul. I mean it's obvious that Infernape would be used. Paul even said that he wanted to battle against Infernape. It's just the others that are in debate and I feel that instead of reserves, it should be the other Sinnoh pokemon.
This is Torterra's chance to shine as well. After being beaten by Paul and struggling to find a style of battling that suits it, this could be where it can use its defenses to its advantage. Not to mention, it could surprise Paul not only because it evolved, but Ash could use his Energy Ball tactics against Paul and I'm sure Paul has never seen that move before. Staraptor already beat one of Paul's pokemon but I think it needs more battles. Unlike Swellow, it hasn't starred in any gym matches or other battles (it has never been the last pokemon standing). And I doubt it would be the last pokemon standing in the Paul match but at least let it get some battles and wins in you know?
Pikachu should finally beat Paul as well. I mean it stuck around throughout the whole Paul vs. Ash rivalry, it'd be nice to see it go up against Paul and win. Sure that didn't apply to Ash's rivalry with Gary but hey, things change and the writing in terms of characters' rivalries have differed a bit. I feel like Pikachu deserves the match against Paul. And then there's Buizel. It just learned Ice Punch, if all the reserves shine in the non-Paul matches, then at least let Buizel get a win against Paul.
The only one questionable is Gible. It hasn't even met Paul and you'd think that Ash could also use Gliscor in the last Paul match. Thing is, if Ash uses Gliscor, he wouldn't be proving anything because another trainer trained Gliscor prior to facing Paul. But Gible's not that strong so how could it help Ash?
I'm not sure how the writers would handle that but I think Gible could have a chance against Paul. It may not win, but it certainly could help out. Maybe Gible can perfect Draco Meteor before the Paul match and it helps weaken one of his pokemon. And I think Gible's a perfect choice for those who think Ash shouldn't use the same pokemon he used in the last 6 vs. 6 battle with Paul because he replaced Gliscor, but still ends up being a Sinnoh pokemon so it's not like a reserve or anything. Also, Gible hasn't even faced a gym so it wouldn't hurt to get in a couple more battles before it may get Oak'd before Isshu.
The Ash vs. Paul is the climax of DP and it would be better if the pokemon involved in Ash's adventure in the Sinnoh shine in this match. So that means his current team (maybe even Gliscor but I'm not sure about that) deserves to face Paul.
All the other reserves can face other trainers. The trainer that owns the legendary, Conway, or any other character of the days that Ash might battle...that's when the reserves can show their stuff. Whether or not the reserves were in the opening, or not, I see them in any non-Paul battles. Overall, I'd really like to have the Sinnoh pokemon have a shining moment as a team and the Paul battle would be the perfect time for that moment.
