RS EHO35, so reliable, easy pull start, sounds like a sewing machine at idle, pulls with authority, putt-putt at 20mph all day for next to nothing.
2-stroke, Tanaka PF-4000, aftermarket mods galore, 50:1 mix means almost smokeless, so reliable, high torque, with silencer not much louder than EHO35 at idle, pulls with EXTRA authority, can putt-putt or go too fast (for a bike) on next to nothing.