AP Miss Fortune is viable, but usually not as the team's main carry. With the proper AP Miss Fortune build, she will deal great AoE damage-over-time using both her E and her Ult. You usually only see AP Miss Fortune played as a support. Even then, it usually isn't better than most other support champions. It can be good against some team compositions and is fun to play, but in competitive play, we really recommend players to stick with AD Miss Fortune.