if you like an ap burst mage, then i strongly suggest anivia, shes way underrated, but can put out amazing numbers and get good aoe at the same time, plus wall is hands down the single best utility spell in the game besides black shield, which is under the nerfscope to be hit with a nerfbat. if you want someone easy to learn, then annie is a safe choice, vlad is buff, kennen has a fantastic early game if you rely on the laning phase to get buff, and veigar is great if they have picked at least 2 strong ap stacking mages that are relatively squishy ( i say relatively because veigar eats ap champs in about 3 shots)

all of these are good choices, but a strong anivia can do more for her team than any other mage champ while still being able to eat anyone that fights her. plus, rebirth, who doesnt want that?

No mundo?

I agree that Anivia is very underrated. I usually play her as a support/dps but she can dish out some serious aoe damage, slow/stun the entire enemy team and block escape or create escape route.

i like to play a AP twisted fate, he does rlly good

Veigar. AP mage without the support.

I'm a fan of Kassadin. You could also consider Vlad who has less burst than say Kassadin or Annie or Anivia but definitely out lasts most of them and his Ult is pretty win for team fights.