Small .26-.30 Saito and OS four-stroke engines are my favourite engines. They are frugal on fuel, doesn't make much noise and provides about the same power as you would expect from a similar size OS FP or LA engine.

I have a SIG 71" Cub that is powered by an OS 26FS using a 10x5 APC propeller. It is built light and flies very similar to a full-size Cub. Admittedly it is sensitive to strong wind gusts, but that's a price I am willing to pay in order to be able to fly around like bumble bee at low altitude during calm evenings. Even though a small capacity engine is used I seldom use more than half-throttle during flight.