Honestly, a lot of people may tell you different, but airfoil really doesn't matter TOO much on a pattern plane. A good rule of thumb is 10-12% for a 2 meter, fully symetrical. Some smaller designs have thicker wings, some as high as 20% or higher. That's a bit much if you ask me. For a 90 sized plane I'd stay around 12-14% with about a 2:1 aspect ratio. Sweep is personal preference, I like my tips 1"-2" swept forward from a straight trailing edge. The leading edges need to be a little sharp to break into a snap cleanly, you don't want the plane to have a 15 deg AOA to stall. Remember, the AMA rules say a 2mm radius minimum. That's actually fairly sharp.

Other than that, just play with it. I believe you'll find wing and stab placement and fuse side area more critical than the actual airfoil. SOme very nice top end pattern planes have REALLY wierd airfoils and don't fly remarkably different than a straight up Symetrical 10% airfoil. If they tell you different, they are usually trying to sell you something.

Designing a pattern plane is a LOT of trial and error. Small changes have a dramatic effect on the way a plane locks on or couples, especially with rudder input. I believe you'll find that the actual airfoil is one of the least important design parameters you have to worry about.

-Mike