Playing Leaf Green, Pearl, AND Emerald at the moment (x_x;
so I'll list all three.
Leaf Green: Venusaur, Charizard, Blastoise, Jolteon, Hypno, Marowak
In RBY and GSC, and FRLG, I like all the starters. Well, I do in RSE too, but not all on the same team, because I like some other early-game Pokés. Anyway, I just used Raichu on my last play, so this time I'm using Jolteon. Also I like Hypno more than 'Zam and I already have Venu so I didn't want Eggy. And Marowak is just my favorite. ^_^
Emerald: Swampert, Shiftry, Breloom, Manectric, Grumpig, Typhlosion
Swampert's my favorite water starter period. Shiftry and Breloom are my two favorite grass-types, and Shiftry's an awesome Chlorophyll-er anyway. Manectric's the only good electric Poké in Emerald IMO (Electrode has sucky special attack and Magneton's 4x ground weak). I've been wanting to use Grumpig for a while since I usually have Gardevoir, and he's actually pretty decent. And I know it'll take a while before I can get Typhlo, but he's my favorite fire starter.
Pearl: Vespiquen, Lucario, Infernape, Gallade, Gardevoir, Vaporeon
Vespi is one of the few bugs I like and a pretty decent tank (Heal Order/Defend Order is kind of nasty o_O). Lucario looks, and IS, raw awesome. Infernape saved my arse against Lucian's Bronzong and he's a flaming monkey, he pwns. Gallade and Gardevoir are two of my favorite Pokémon and are pretty versatile. And finally, Vaporeon is my third-favorite Eeveelution (after Leafeon and Jolteon), and I really needed a Water-type.