Much more info and additional links here:
24" advocates

I have not packed up a 20 inch folder into a suitcase so I can't compare, but I can say that it takes a lot of time and effort to pack up my 24 inch bike.

Also consider S&S coupled full size bikes or Ritchey Breakaway full size bikes. The Ritchey case is oversize but the owners that I have talked to were rarely charged the oversize fee.

Bikes that you can pack up for travel in a small case, are compromises between portability/transportability and ride-ability. Only you can judge how much time and effort you want to put into assembling and later re-packing a bike and how that compares to your enjoyment that you get from riding it.