top tier eh? that's a tough call considering that there are only what, 12 mages? 15 if you count all the wizards? I suppose I should pick the top third, (4 or 5 mages).
1. Wizard (water) = Just too good at the undoing game. whatever you do, he can undo, twice. I wont get into why Wizards of all sorts are superior (perhaps unfairly so) as that topic has been destroyed here, but with all the options open to them wizards are probably the reason for this topic in a roundabaout way. nuff said.
2. Druid = My personal favorite mage. i think she handles the nature school so much better than the beastmasters. add her super efficient creatures, and her unique vine abilities (extended summon range, hinders the unhinderable etc) she currently has almost as much versatility as a wizard, and that's with TWO 3x schools. awesome mage.
3. Priestess = She probably has the strongest mage abilities (read consistently useful) of any of the mages. the ability to remove conditions without having to book anything for it is AMAZING! even of the spells that remove conditions are in school (purify, healing wand) you don't need them and that makes room for another enchantment (i like enchantments, and parentheses which, at this point, should be blatantly apparent) or what have you. her late game is incredible, and even if your games go to time she can burst heal for ridiculous amounts reliably, making it difficult to attrition your way to a win there. as a side note i really like the priest, i am dedicated to making him a viable choice! he just feels so badass and i wish i knew why most people find him to be one of if not the weakest mage.
4. Forcemaster = Personally i don't agree with this. but her results in the hands of other (likely vastly more skilled) pilots is impossible to argue with! if you completely ignore the creatures in the mind school, her spell selection is pretty awesome. if you can somehow keep the enemy mage as action starved as she is likely to be then you might be in business. she is the absolute queen of the aggressive rush, with a unique weapon that never really goes away, and a potentially amazing familiar (they are damn squishy though,them thoughtspores), and you can splash for a good buddy out of school and it doesn't hurt TOO bad. i cant make one work to save my life, but that's a personal failing i guess. shes tricky, but definitely powerful if done well
Honerable mention: AC Warlock. = If the forcemaster is the queen of the aggressive rush, this guy is the smoldering, angsty king. hes not top 4 in my case because fire is, almost by default, teched against in every build. its almost stupid not to. but sometimes, even when you are ready for the assault, those fireballs and curses make too steady a damage stream to overcome. escalating damage is his specialty, but just like any good bonfire eventually he runs out of fuel. His bet is that hes got you reduced to a heap of ash before he runs out of resources. and hes tough enough to continue to press the assault even if you match him point for point. hes got more life than you. Couple that with the dark school being freaking awesome and he is a very fun mage to play! thats probably why he didnt make top 4, hes more fun to use than reliably victorious.
Anyway thats my take. hope it was useful! i know these are kind of general descriptions but that was kinda the idea. I love this game. Its awesome.