I'm quite surprised that the Siren is not on this list; mind you her life is quite low....
Best Mage: I would have to go with a top 3 on this one
1- Forcemaster: You wanna win a quick game and guarantee that your opponent has no control? Forcemaster is your best option, with pretty much all you need to make sure your opponent stops dead in his tracks. If you're quick/efficient enough, you don't need to worry about creature swarms too much. Only major weakness is a opponent wizard who's filled with Arcane spells
2- Druid: Plants are limited yet so powerful. So many available options, with your only major weakness being fire, although this is easily bettered by almost everything you own having regenerating traits. Definitely a powerhouse in my books
3-Siren: Surprised that she isn't on this list yet; all you need is some shallow Sea, Crocodiles, the Sherean Leviathan and the Kraken and you are an immediate threat, no matter you the opponent is playing as. Only issues I have are her low life and mana, as well as the fact that the designers did not give her any triple costs for fire spells (why I do not know....)
Worst Mage for me has to be the Bloodwave Warlord; just a bunch of basic military units with no special characteristics, and besides for the tough equipment that he has there's no much more that can help his cause.