Depends what for, and style of play.
AOE levelling? ST levelling? Best DPS end game? Support DPS end game (winters chill)?
30/0/20: Arcane build, still using Frost Bolt, best DPS spec for raids/dungeons. Not many points you can swap around here.
16/0/35: Winters chill, you should have 1 mage with this spec in your raid. More freedom to swap some talents around here, for example I don't like going so far down the arcane tree here. This spec is more fun in dungeons, as you have more survivability.
For levelling, I would recommend going aoe spec, it's fun and unique. Want to play ST levelling? Play another class
That said, you can ST level just fine in an aoe build.