RE: 2 Stroke vs. 4 Stroke
Two strokes are usually cheaper to buy than four strokes. They have less moving parts and are generally considered 'easier' for a person new to the hobby to operate.
Some, not all, two strokes run well at idle and full throttle but not so well at half throttle. My Thunder Tiger 61 never ran well at half throttle but my ASP 61 does.
All of my four strokes seem to run well at half throttle and all other settings.
My .61 two stroke burns more fuel in a 10 minute flight than my .91 four stroke. Many people believe the .61 two stroke and .91 four stroke are fairly equivalent in performance.
A totally subjective point; I think four strokes sound better than two strokes.