Gen I and II would have to be my favourite generations of Pokemon.
Personally, I love Crobat. I think it's great. I've always had a bit of a thing for Pokemon with lots of speed (which usually means I pump up the slower ones with Carbos, haha).. Yet I also really liked Wooper/Quagsire.
Other favourites of mine:
*Eevee and the eeveelutions. Specifically Umbreon, Jolteon and Espeon. Umbreon has always been #1 in this line, but Jolteon was my beast on my most recent play-through of Red Version (and E4 MVP). I was originally never a fan of Espeon, but I have to say, it's growing on me.
*Growlithe/Arcanine. LOVE these guys, though somehow I've always managed to have the version that doesn't have them in it. Until I got W2!
*Ponyta/Rapidash. My replacement for Arcanine in pretty much every game I can't get it.
*Ditto is just a little cutie, Dragonite is great, and Ampharos was my electric type in the Metal Generations. My crush on Jasmine totally didn't influence that decision.
*Teddiursa is awesome. Pretty sure I try and catch one in every game I can, just to keep it in the PC (and generally I don't go out of my way to catch Pokemon - usually just pick up a 'key' team and the event ones along the way).
*Hitmontop has a really awesome design, I think. Though I never was able to catch one..
Finally, Suicune and Lugia are also pretty strong favourites of mine. Suicune because I had a love affair with Crystal when I was growing up, and Lugia because of Pokemon the Movie 2000. Best kids movie I've ever seen.