Kill them quickly before they attack you with their strong magic combos, they are usually found in groups with other Minotaurs, so Avalanche, GFB or Explosion runes are quite useful to have with you. They are resistant to Energy Damage so keep in mind that those spells won't hurt them much, neither will Earth Damage spells. You may consider to use Invisibility or a Stealth Ring if there are many Minotaurs, as only the Minotaur Mages can see invisible players.
Mages: with a decent Magic Level (around 35), can kill them easily by just rushing in and using Ice Damage spells. This stratagy kills them quickly, and uses very little Mana.
Knights with a weapon skill of about 55 can kill them in under 5 hits with a decent weapon (e.g. Dwarven Axe). Just watch out for the Energy Field spell they cast which can cause great damage if you don't pay attention.