Frost is pretty good, at the lowest levels you're simply looking at what spell you most recently got, since it will most likely put out the highest DPS.
For many, Frost provides the best grinding all the way up into the 60s, because it offers relatively good mana efficiency, decent-to-excellent dps with crits, highly effective defensive techniques such as Ice Barrier, and in many reguards the best AE options.
There are going to be points where you're stuck doing slow grinds and quests, and quite honestly for your instances on your trip up it's going to be hard to match the effectiveness and utility of Arcane/Fire Mages, but Ice definatly can keep up with the damage, and depending on what type of group you're rolling with a Blizzard here or there can be insanely high DPS and DPM and utility.
For the AE grind and the "difficult" quests, as long as your Playstyle matches it I think it's safe to say that Ice is your best bet.
Common All-Around Ice Build - Ice is really the only tree that works almost entirely in it's own tree... with this also comes the fact that it is much more single-element dependant, and for single target DPS extremely reliant on crits.
As for myself, I'm leveling with Arcane right now, and I love the Rambo-ish style of the build. I definatly respect a good Ice build though, and with Ice you feel the rush of having total control over your targets while still having those extra defensive techs to fall back on.
Edited, Oct 8th 2007 4:11pm by tzsjynx