Gyarados was boss in 1st gen. Dragon Rage early on made it incredibly easy to train, and it could have a lot of Special moves which ran off a decent Special stat. 2nd gen ruined it, 3rd gen gave it a little back, and 4th gen turned it into an awesome powerhouse. Really, in HGSS, the red Gyarados will get you through the game without problems.
Purrloin was one of the worst Pokémon I raised. Weak and dies easily.
Zubat is also a pain to raise until it learns Wing Attack right before it evolves.