Kass is always banned in games I play. Galio surprisingly draws rage in mid lane, despite how absolutely great he is at it in this metagame, and frankly I just don't like the headache of getting yelled at. I'll try Ryze.

I beat Ahri about as often as I lose to her right now; I know how to play against her just fine. If I'm better, I win, if I'm worse, I lose. I still want the best possible matchup to try and shift things in my favor though.

best ahri counter is ori

I would say Kassadin or Ryze. They are both really good champs who can deal with her harass as long as you have the mind to side-step her skill shots.

The best way to deal with her is to try and abuse her before she hits level six when she reaches the near ungankable stage. If your jungler and yourself can break her down before she gets her ult then you should snowball on her.

A friend of mine has been blasting middle champs like Ahri with AP Master Yi. It supposedly works really good. He does good with that, I wouldn't try it myself. But give it a shot! :P

Kass. or Cass Lol

People are giving you a wide range of champs for counters....I play Ahri as a main and have done so for awhile now. I will list you some champions and give you reasons why they "can" beat Ahri.
here is the list with reasons tagged to each just pick according to your play style: 1. Brand (range harass early is good + the cc that is needed vs an aggressive Ahri his very nice)
2. Malzahar ( he can keep his distance and still push creeps, if Ahri charges while ult is available 9 times out of 10 Ahri is dead)
3. Karthus (like any karthus playing it safe in 1v1s is a good idea however build for hp/ap and Ahri cant do anything to you alone except harass.)

The follow are champions I suggest to avoid midding vs Ahri with: 1. Leblanc (while being a great burst ap her main harass ability puts her right in the path of Ahri's and early game that will prove fatal.)
2. Ryze (while Ryze is known for being a good mid with the ability to keep enemies at a distance vs Ahri his only precaution is his snare, this is easily countered by Ahri's taunt ALSO Ryze's snare does nothing to keep ahri from dealing out dmg) SIDE NOTE - any champion that uses snare is in the same boat as Ryze.
3. Heimerdinger (while being a great mid pusher and burst early game still goes to a good Ahri and if Heimerdinger cant hold his ground then it will snowball fast.)

Any other advice vs ahri just ask.

I never have problems with Ahri, as Ahri pushes her lane so easily when she misses her Q.

1 - Kassadin, the infamous counter to AP mid.

2 - Talon, his high damage early on along with silence make him a great choice against Ahri.

3 - AP Master Yi. It actually works, if you time Meditate correctly, aka don't Meditate until after the Charm.

I agree with Ksasadin. Silence is devastating against caster champs that are mashing QWEREWQWERWEW etc. Remember her orb does TRUE damage on the way back- the difference is really noticible late game when people build some MR.

Swain.....