As my AP Mids, here are my two favorites:
Kassadin: If you can get past levels 1-5, you can easily grab kills. Once he reaches level 6, he is pretty scary. You can secure kills with your rift walk, jump out of tough situations, and do some pretty scary ganks. He can 1v1 with some AP Mid champs pretty well (Karthus, Fiddlesticks, etc). I main Kass so here is some advice: Through levels 1-5, harass your opponent and keep them at half health. Once you reach level 6, go in for the kill with R>Q>E>Ignite>W>Auto attack combo and you should be able to get the kill. Recall back and go roam. Grab a few more kills, win the game, GG.
Katarina: A very easy champ to use. Her ult is amazing in team fights, and her passive makes it easy to clean up. Make sure to carry around wards with you as you can E to wards and escape safely. She also has a very painful early game like Kass.
My favorite AD Mids:
Talon: Has a blink and silence, a DoT buff, and a pretty good ult in team fights. He's good against roamy mid-laners (Kass, Kat, Ahri).
Wukong: Not seen mid much, though is viable. I don't have much to say since I've only seen colbycheeze do it. Definitely looks fun though.