1st gen (Yellow): Misty, Pikachu use Thunderbolt! xD
2nd gen (Gold): I can't remember, maybe Bugsy?
3rd gen (Ruby & Emerald): Roxanne, Mudkip (well Marshtomp, I tend to overgrind xD) use Mud-slap! xD Use Water gun! xD xD
4th gen (Diamond and Pearl): Roark, Rock type normally tends to be easiest for me (Twiggy, Turtwig xD)
4th gen (Heartgold): Believe it or not, Whitney. Clefairy? Geodude, Rock Smash and it worked. Miltank? Geodude, Selfdestruct. Like 3 or 4 moves xD
5th gen (Black): Maybe Clay, because like Rock, Ground tends to be fairly easy for me.