Most Helpful Girl
Okay, I have like three favourites :P
For sentimentality, Eevee is my favourite. It was the first pokemon I got really attached to when I was little, I loved it, I still love it, I think it's adorable - and I won't ever use it in my team because I can't make it into a battle-worthy pokemon.
Of the Eeveelutions, Sylveon is definitely my favourite. I actually love battling with fairy types and Sylveon is so good, I love it (I got a shirt a while ago that says 'Be cute. Be sweet. Slay dragons.' around Sylveon's face with lots of poffins around it, it's adorable) <3
And my favourite pokemon to actually use in battle is most definitely Banette. I adore fairy types but ghost types are my second favourite and have a special place in my heart and Banette is such a badass, I just love using it. Plus, look how amazing it looks <3
(Also special shout out to Mega-Banette because it's creepy as fuck!)
Most Helpful Guy
Although I had stopped playing the games long time ago I remember I liked using these Pokémon characters the most:
and all 3 of the Legendary Birds;
and sometimes Gengar or Dragonite
Didn't play anything after red and blue so I'm unfamilar with the rest.
But I heard Arceus is the best out of all Pokémon if you want to play to win in the later games or something like that since it was considered the most powerful if not the most Overpowered Pokémon.
Either way, my point is that the MOST powerful and consistent in the original two Gameboy games were the most memorable to me. As they helped me beat the last 4 or 5 bosses with the least amount of difficulties and frustrations in the shortest time possible and finish the game.