mareep/ampharos it just really good. awesome speed and sp atk, decent defenses, and that's the combo you want in pokemon. also the nostalgia factor plays a big role...
I think scizor is a really excellent pokemon too. no more weakness to flying or to ice or to rock. gains a weakness to fighting, but it's defense is so high it doesn't matter. and the fire weakness it already had, plus most fire attacks being special means they would have killed it anyway. and then high attack, and technician ability makes it crazy good