I think that Superboy, Wonder Girl, and Kid Flash has more enemies than anyone...
Superboy: Match, Lex Luthor, King Shark, Knockout, Scavenger
Wonder Girl: Lycus, Ares (reluctantly), Devastation
Kid Flash: Inertia/Kid Zoom, White Lightning (come to think that White Lightning is the only recurrring villains..hmmm - will have to re-read the whole old issues of Impulse.)
Ray - Dr Polaris
Jessie Quick - Tigress, Baroness Blitzkreig
Damage - Dr. Polaris, Vandal Savage
Tempest - Syrene (Siren?)
Donna Troy - Red Panzer
Robin/Nightwing - ?? Lady Vic ??, Deathstroke?, Blockbuster II
Robin/Red Robin - Talia?, Ra's Al?, Charaxes
Anima - can't remember....
Cyborg - Cyborgirl?
Starfire - Blackfire (of course!)
Miss Martian - Sun Girl