I've gradually increased the number of Pokémon I use in my team. When I first played Red, I just used Blastoise. In Gold, I developed a team of 5, but I only finished adding the last few members after I beat the game. More recently, though, I've found that I've tended to use more than six Pokémon at a time, and I rotate them in and out. In BW, I trained most of the Pokémon I caught (thanks to the experience mechanics that made it easy to level up low-level Pokémon), and in X, I have a team of 10-12 main Pokémon that I used in-game (with lots of additional ones bred competitively since beating the Elite Four).