=== Gen 1 ===
My lineups of favorites back in the day:
+Blastoise - First starter, continued to use the same one for about 4 or so playthroughs and he got a little abusive.
+Raichu - The guide told me that Pikachu could be found in the Viridian Forest, and being a kid I decided that nothing could be cooler. My Pidgey was practically evolved by the time I caught one. Never thought twice about evolving him the first moment I could. I like Magneton more these days, but it is a tough call sometimes.
+Venomoth - I always liked Venonat's design, and after Butterfree frustrated me to death I switched. Much more success was had at putting my friends to sleep.
+Kangaskan - Giovanni had one, so of course I had to also. I still claim it to be the epitome of awesome, though I wish they hadn't gone the route of making them all female and fleshed them out a bit more. :/
+Pidgeot - Said Pidgey from above. It grew on me.
Asking me now:
I would swap Blastoise with Tentacruel. I always assumed the most common guys wouldn't be anything more than filler, and he was weak to psychic, but Tentacruel has probably jumped into my top 3 all time favorites since. Keep Venomoth and Kangaskan, they're still rocking out. As for Pidgeot, he has lost his place to Nidoking once I realized that I could get one early on that west path. Versatility plus great looks nets him a top spot.
=== Gen 2 ===
I've always been a stickler for using what already know I like, but these guys got some legroom:
+Dunsparce - Remember browsing a magazine at the grocery store and seeing this little demon. Don't know why I liked him, but that doesn't matter much does it?
+Ampharos - Do androids dream of electric sheep? Bit of a sci-fi fan.
+Ariados - Used him a lot on my first playthrough, but kinda phased him out. If only he were a little.... something more?
+Yanma - The reason I phased out Ariados.
+Octillery - Always did think cephalopods were cool. This guy and Dunsparce I would put on any list of candidates for an evolution.
=== Most Hated ===
+Golbat - Don't get me wrong, I use them on my teams time to time, but between being kinda spooky looking and constantly present.... I hate to stare.
+Chancey - Thought it looked pretty lame, so I made a specific point of burning them up when trying the cloning/trade tricks.
+Mewtwo - Because everyone but me felt it mandatory to include one on the team. My only solace were those who caught them as a super leveled glitch and forgot that it only knew support moves.
+Moltres - The only of the bird trio that I didn't really understand how to use.