Mages (from the revised edition of Elements of Magic) are better than wizards because they can make their own spells up of whatever power level they need at the time, and they can learn healing spells. Plus, they're not tied to a Vancian-esque preparation ruleset, so you can learn any sort of magic from whatever source you want. And you can kill people with Time*.
* or Acid, Air, Balance, Chaos, Crystal, Death, Earth, Evil, Fire, Force, Good, Ice, Lava, Law, Life, Light, Lightning, Metal, Mist, Nature, Ooze, Shadow, Sound, Space, Void, or Water.
For Mages vs. Clerics, as above, except replace 'they can learn healing spells' with 'they can learn powerful attack, illusion, movement, and transformation spells.'
For Mages vs. Sorcerers, as above, except replace 'Vancian-esque preparation ruleset' with 'limited selection of spells.'