A lot of people will tell you it's the GP Ultrasport. I have the kit but haven't built it yet so I have to take their word on it for now. I really like the GP Super Sportsters both my .40 and .60 size are great. Well, the .40 WAS... Another good one is the World Models Rambler .45. It comes with retracts, flys like it is on a rail and lands near as gently as a trainer. It's currently my most flown plane.

Come to think of it, they're all cool. I think I will keep buying and building them all in a never ending search for the best.