Empoleon... this is sad but true, saying my first level 100 was a Generation 4... but the only other Pokemon game I had played before then was Yellow and I didn't have it long enough to raise any to level 100. But since Empoleon was super effective against ground and fire and those were two of the types of the Elite Four, through some massive grind I eventually got it. My next one that I'm going to get there is either Giratina, Typhlosion, or Alakazam.
Also, Typhlosion is my all time favorite Pokemon. Typhlosion fans, unite!