I prefer a 21-22" suitcase with a fold out garment bag. Personally, I prefer the Victorinox series of luggage (kind of pricey, but built very sturdy).
The last several trips I took I had to randomly check my carry-on at the gate. I'm not sure how often this is happening but basically since airlines charge for check-in luggage, everyone has migrated to carry-ons --- what ends up happening is there isn't enough space on top for everyone and they end up checking your luggage at the gate anyway (although at no cost). For this reason, I would be hesitant to use anything nice and that is not indestructible.