RE: Favorite engine?
Absolute favorite -- a lightened G62 on electronic ignition. They just never quit. Never had to have one serviced for any reason.
2nd favorite is any conversion engine 35cc--100cc with electronic ignition. Reliable, cheap, powerful. Not any heavier than your average Sachs based engines if done right.
I really only own a handful of gassers. I have 4 or 5 Zenoah G62 engines lying around. I have a 54cc Poulan, 60cc Poulan, Fox 3.2, Craftsman 36cc x 2, Stihl 75cc, Stihl 110cc single, a dozen or so Ryobi 31cc and 28cc engines and one weedie thats 21cc but I don't know what make or model it is.
I like all of them. Each has an application best fitted to it's individual performance.