hmmm.... interesting... instead of commenting on previous posts, i'm going to just start afresh:

2-strokes
simple mechanics =
less temperamental
less maintenance
lighter engine
combustion on the very stroke =
higher rpm over higher torque

4-strokes
more complicated mechanics =
prettier to look at (particularly open rockers and saito hemis)
more rewarding to work on
combustion on every other rotation =
more efficient on gas
more complete burn (no exhaust gases)
deeper more pleasant exhaust note

overall the 4-strokes of the same displacement will turn a prop larger than a 2-stroke at the same RPM. yes 2-strokes can turn a tiny prop at huge rpms but for all around tractability, a 4-stroke will kick the pants off a 2-stroke. I would assume that's why most 3D and F3A prefer 4-strokes over 2-strokes. just my two cents.