Oh, I got hit with the nostalgia seeing this thread! Ruby was one of my first games as a kid and my introduction to the Pokemon games, so I'm gonna recall my very first team (and other first playthrough Gen 3 games)
There's 4 very distinct Pokemon I remember using for my main team (note: I still have these 4 with me! I've been transferring them up the ladder cause they have a lot of sentimental value to me). I don't think I used a full team of 6, as the other 2 were for HMs.
1. Blaziken. My first starter ever. I love Blaziken, it was "my" Pokemon for a long time. I remember running through the E4 over and over again to get it to lvl 100. Even did a solo run of the E4 with it! He was also my ticket for beating Sidney, Glacia, and Steven.
2. Banette. I loved the idea of a haunted doll as a Pokemon, and as a kid I needed a counter for Phoebe. The second Pokemon I ever got to lvl 100.
3. Glalie. My counter for Drake. Also loved the design so I had to put it on my team. The 3rd Pokemon I got to lvl 100.
4. Crobat. More-so the Fly user on my team, but the speed of Crobat was cool. Plus Crobat is cool in general. All my Pokemon in all these years have mainly been chosen by looks, not stats lol. I remember using PP Max on Wing Attack so it had like a ridiculous 64pp on it or something like that. The 4th Pokemon I got to lvl 100.
At this point I just had some throwaways for HMs.
1. Zigzagoon/Linoone. Pretty common for most people I think, it just really works.
2. Tropius. Primary Flyer. Eventually replaced with Crobat.
3. Groudon. I remember putting Cut and Rock Smash on it. Don't ask me why lol.
4. Nuzleaf. I very clearly remember a very low level Nuzleaf beating Flannery for me and hogging all the Torkoal exp. I have no idea how a low level Grass type beat a Fire type gym, but it stuck in my memory, so Nuzleaf gets the honorary mention.
Leafgreen was my other "main" gen 3 game. I had Sapphire, Emerald, and Firered, but they were my resetters, AKA keep all the cool stuff on my main game and play through the other version when I wanted to play Pokemon... which was a lot.
My Leafgreen first playthrough wasn't nearly as cool now that I think about it, I did the dumb kid thing where I basically only used my starter throughout the entire game.
1. Charizard. Beefy boy could Flamethrower, Wing Attack, and Slash everything in sight, so he would just powerhouse me through the game. The only problem was Lorelei once I reached the Elite 4. Charizard wasn't cut out for that, so I had to grab an alternative.
2. Zapdos. Luckily we got a powerful Electric type Legendary in our hands. I remember having to teach it Shock Wave through TM cause it doesn't have any Electric attacking moves when you catch it.
Those are the only 2 I distinctly remember using in my first playthrough. Leafgreen is fuzzier than Ruby for some reason. I couldn't even tell you what I used for HMs back then.
Aaaaand since Colosseum and Gale of Darkness are Gen 3 games, I'll mention those too.
Colosseum was a really, really hard game as a kid. I remember struggling through it so much, especially near end game. I think a lot of that was due to my team choice lol.
1. Umbreon. Pretty natural choice since you start with it, however I scrapped Espeon and left it in the dust since Umbreon was my favorite choice. I did not know that Umbreon is primarily a defensive Pokemon back then and Espeon was the attacker. Probably explains why I had a hard time lol.
2. Entei. Fire type legendary powerhouse in the early game? Heck yeah I'm using that on my team! Entei became my main attacker throughout the game. I remember a friend telling me to grab Croconaw and Quagsire and purify them because you "absolutely needed to" for Entei. Those two stayed on my team throughout most my playthrough, but never got any levels beyond Entei's fight.
.... Yup, that was it. Everything else was usually just whatever Shadow Pokemon I recently got. Did I mention the game was hard for me as a kid?
XD Gale of Darkness was just as bad in terms of the team I used, but the game was easier in general.
1. Umbreon. Yeeeah, I chose Umbreon for my Eevee instead of literally anything else that would have helped more or been a little more unique than the Colosseum options. Oh well, I still love Umbreon.
2. Houndoom. Early game Houndour catch, he kinda became my "in spirit" Entei. I guess I just wanted to recreate my Colosseum team, idk what I was thinking lol. Houndoom is cool though, so I can't blame my younger self (Also the double Dark Pokemon team? Well, it worked out pretty well from what I remember).
.... Why use a full team of 6 when you can just use two for the double battles??? *nervous laughter*