Whomever said negative things about 4 stroke engines didn't really know what they were talking about. 4 strokers are prime in r/c. I have a TT.91FS in my 4*60. I'd recommend the 4 stroke simply for the power (ability to swing a larger prop with the added torque) sound and little fuel it uses. Choice is yours. As far as maintenance, I've been flying over 7 years and own about 8 four strokes maintenance is next to nothing. Every now and then the valves may need to be adjusted. Again, "may" need to be adjusted.

Good luck.