I main Kennen, and he is extremely fun.. hard to master though.. i suggest playing a bunch of practice games before joining a real game.

Anivia is also hard to play, but not as fun imo.. still a great champ. Anivia has more support because of her wall.

Go Anivia. I learned the basics of being a good player by playing her even if I kept losing. Positioning, timing, predicting channelling spells to stun and such. She'll be hard at first but if you keep going you'll become a better player overall.

Anivia is incredible, when played well.

Good use of crystallize separates a good Anivia from a great one.

Kennen because Anivia is free next week.

Kennen is fun indeed but Anivia can wreck some games if you can play her effectively. Just depends on your preference (after all, one has an energy bar and the other has mana).

I prefer kennen because he's a nice change of pace