I bought an UltraStick 40 ARF. I was originally planning to toss a .46 2-stroke engine in it but instead went with a Saito .62 4-stroke. It's hard to compare power since with one you're spinning a 10" prop at higher RPM and the other, a 12" prop at lower RPM.

The 4-stroke is definitely quieter, more expensive to purchase, not really that much more difficult to set up plus it just sounds way better.