I can’t speak for PvP, but for PvE.
Fire dominates all forms of top tier content assuming that the group plays around combustion.
Frost/Arcane can hold their own though, and don’t require the group to play around you.
If you’re trying to reach the tippy top, then fire is the way to go. It’s VERY gear reliant by comparison, and has a higher skill cap out of the three. And note… by tippy top, I mean you’re gunning for +20 and above keys, and pushing your CE rank (not just getting CE… but getting a good rank for CE, for which you’ve already missed the boat on that). Not doing that? Then play what you enjoy.
Frost has 3 builds:
Standard GS: decent all round build
No IL: Best ST, ok AoE
Orb build: Best AoE, ok ST
Arcane is supreme ST (better than fire) assuming you can plant your feet and turret.
Arcane requires you to swap up your talents (I think, tell me if I’m wrong here arcane mages) for AoE, which severely impacts your ST.
Fire… Well fire is strong at everything right now. Excellent ST, huge on demand burst, fantastic AoE built straight into that burst via ignite, and ok AoE outside of that burst. It’s ST outside of combustion is pretty meh though.
If you want an example, when I 5 mask my horrific visions… most bosses (save thrall/alleria) die before they cast any of their abilities when I’m on my fire mage. Everyone complains about Rexxar’s boars, but for me… he dies before the first set get their first cast off (or at least soon after).
Edit: Oh and I just want to add… double on use is making me hate my fire mage… No Mr Tank… you have to pull RIGHT NOW… GO PLEASE… annnd I got like 3 seconds of overlap… fml.