As others have said, back in the day I really only focused on my starter so my first level 100 was my Charizard from Blue which was the first Pokemon I ever chose. Then for the battle against Red in Gold I trained both my Typhlosion and my Ampharos to 100 to help cover his team. Closest I've got since then is my lv85 Blaziken in Sapphire.
I know. I have a thing for Fire starters. >.<