Anivia Masteries: Offense or Utility?

Anivia is one of my old favourites. Recently, a user named Unholy Wish posted an intriguing thread about how he/she accomplished the phenomenally difficult task of getting about a 40 win streak in ranked games as Anivia.

This inspired me to revisit Anivia. One of the interesting things is due to the Season 2 changes, she now has choices for masteries.

I've stuck to 9/0/21 for Anivia as Utility provides a huge host of benefits, while offense only serves to increase damage through ability power. In my opinion going Offense means a larger reliance on getting a good lead to get AP items. Utility helps make up for her lackluster early game while also providing other benefits useful throughout the game, such as mana and regeneration, increased experience gain, longer buff duration, shorter cooldowns on both champion and summoner spells, etc.

What do you prefer to get on Anivia: 21 in Offense or 21 in utility? Perhaps something different?