What type of flying do you want to do? Sport? Scale? Warbird? Aerobatic? 3D? That will determine what 1/4 scale airplanes are out there and what engine would be suitable.

Do you already have the 28cc gasser? If so, check out the "25%" planes from Cermark. The aren't technically 25% scale if you wanted to be nit-picky but that's no big deal. I have the Yak with an MLD-28S and it is a nice combo.

I also have a GP 25% Sukhoi that flys nice but it definitely needs a larger engine. I have a 43cc on mine.