Best to worst as far as "sound" IMO.

4-stroke gas/methanol preferably methanol W/CDI. Gas 4-strokes tend to be a bit low on power & glow ignition wastes about 25% of the fuel .
2 stroke "gas" (if they are suffeciently "muffled" to reduce the "chainsaw" effect)
2 stroke "glow" (not much btter than electric IMO)
When they start powering full scale aircraft W/electricity on a production basis then electric would be a consideration in a scale version of said aircraft.

While few full scale aircraft are powered W/2-stroke ICEs, the bending of the true type of ICE is somewhat acceptable to me, but since MOST are powered W/4-stroke ICEs that is what I prefer.