4 strokes are not as good because they do not have sufficient oil in the top end on cold start ups (in our canadian winter) and exess wear can occur if not properly warmed up. 2 strokes are the best desighn as long as they are warmed up because the oil mixed (or injected) in the gas is always lubracating the piston ring etc, as soon as it is fired up. Also 2 strokes can handle higher RPM then 4 strokes because of there design, 4 strokes have valves, which is the main reason for the low reving capabilities. 4 strokes are a more "bottom end power" designed for high stress situations (trucks,cars etc) 2 strokes are snappier, and rev up alot higher, and in my opinion, seem alot more reliable as long as the gas/oil ratio is properly mixed and the engine is taken care of.

Hope this helps.