A Conundrum

Bigger scale models are more fun to paint.  Smaller-scale models allow more movement, and are more fun to play.

28mm models are the standard for most wargames now; big enough to be interesting to paint, not so huge as to be completely ridiculous.  (Like 54mm). 

But, honestly, I think 28mm is borderline too large for a satisfying game of maneuver.  I prefer the game play with 15mm or 10/6mm.