picking a "best" combat plane is hard, part of the decision is your particular style of flying.

You also didn't mention what class of combat you'd be flying. If you're flying Open B or C, then you'll want as much wing area as you can get. I haven't been to spadtothebone in a while, but I did see someone post some pictures on (I think) the RCCA site, rccombat.com, of a spad-falcon (Spalcon?). Going in that direction would seem to be a good idea.

The Sickle/Gremlin flying wings are fairly effective as well. Fast and light, they work well for some folks.