I don't have favorites by generation. What I do is give myself the perfect team of six pokemon, and fill it. If I find one that I like more than another in the six, I switch them out. However, my current team hasn't changed in awhile, so it may not for awhile it goes like this:
1. Blastoise. Squirtle is my favorite starter of all time, and I think Blastoise is awesome overall.
2. Machamp. Not sure why, but I always catch a machop if I can, just so I can get a Machamp.
3. Alakazam. There's nothing more satisfying to me than getting abra to learn an attack so that I can train it on its own. Alakazam is probably my favorite overall, just because it's attacks and design are amazing.
4. Umbreon. I think I really like Umbreon because until I was about 17, I never could get an Eevee in my party until the very end, when it didn't matter to me. Then, I played Heart Gold, and got one, and evolved it into an Umbreon. Umbreon is the coolest Eevee evolution to me because Umbreon is the only dark Pokemon that's mysterious rather than intimidating, and because I really like its look.
5. Lucario. BECAUSE HE'S FRICKIN' LUCARIO. And I really like the steel/fighting combo.
6. Luxray. Luxray is probably the weakest out of these six in regards to my likes, but I like him because strong electric types are harder than normal to get, and a lion in my party is awesome.
Seriously, if I was on the dev team for a pokemon MMO, I would have these six pokemon, and just wander the world map and challenge random people to battles.