I started with 1st and skipped 2nd; I got back into the franchise with a copy of FireRed I borrowed from a friend and have played each subsequent generation since then.
Maybe it's because I skipped it when it was on the Game Boy, but I played HeartGold/SoulSilver and didn't find 2nd generation all that good. Don't get me wrong, I still loved it but I fail to understand why people love it so much. I made the (apparent) mistake of trying to do too much of the quest after I beat the Elite Four the first time (instead of XP grinding them for a while), and they leveled up their Pokemon in my absence. With the lack of a Vs. Seeker and very, very few wild pokemon above level 50 to grind, I actually stopped playing with my team in the mid 50s, unable to beat the updated Elite Four and not interested enough to grind on lower level wild pokemon until I could take them.
I'd have to say my favorite gen was 3rd; not because I think it was the best (I can't pick a "best generation"), but because it had a good mix of nostalgia (with FireRed/LeafGreen) and newness, with Sapphire/Ruby/Emerald. And because all the DS games are slow as hell when it comes to moving between menus, saving and fighting.