Still competitive at the Sportsman and Intermediate level, after close to 30 years... the Sig King Kobra. It will build quickly, relatively easilly, and not cost an arm and a leg.
(Kougar and Kobra would do OK too... but they are smaller versions of the same plane)

Work to keep it light... all too easy to come out heavy enough to impair performance. (common problem with any competition aircraft...)

Actually, at the Sportsman level, flying skill is so important that you could almost compete with a trainer. Practically any aircraft that has reasonable tollerance for the turbulent conditions found at some fields will work. "Stick Clones" and similar have been known to place well. I've even seen a scale model .60 size Cub flown n Pattern competition and do reasonably well at the Sportsman level.

You don't need to get one of the $1000 kits to get started... just to go into the upper levels of competition, you better have a plane that is top of the line. (and about 5 to 10 years experience in competition flying...)