Oh man, that's hard to remember. I know it was in my Blue version though, because heck, it was the only game I had at the time, so I spent a lot of time just training the Pokemon in that. The question is just whether it'd be considered legit or not, since it was a game me and my brother shared, so the training was mostly half/half, and I honestly can't remember what I trained and what he trained, so yeah. It was most likely my starter though.
One Pokemon I know for certain though, which also explains my love for it today, was the Pidgey I caught in my Silver version. It's the first Pokemon I can recall legitimately getting to 100 all by myself, so Imma say that one just for the sake of it :p I wasn't so obsessed with getting my Pokemon to 100 in that game though, because I really enjoyed playing through the story, so I restarted often. My brother on the other hand, was not only trying to catch 'em all, he was also trying to train them all to 100, and he actually got really far with it all. I don't remember how many Pokemon he actually got to 100, but I'm pretty sure it was over half of them. He eventually grew bored of it though, and didn't play the game for years, and when he finally decided he wanted to try out the game again, the battery on his Gold version had unfortunately died, and all his progress was lost :( I guess I was lucky my friend lost my game, otherwise I might've experienced the same thing ;D