Depends entirely on the character. Some characters do wonderfully in the air, while others do better on the ground or close to it. Every character has to take to the air eventually though, so having one that can at least attempt it is a plus.
For instance: Wario is mostly all air. When he attacks on the ground its highly punishable, laggy, and most likely an attempt to KO. Wario's probably stay in the air a good 75%+ of the time.
Snake however, is mostly campy and on the ground. When he does go into the air, its either to KO with U-air or B-air, or because he was knocked that way.
My Creations in Modnation Racers! Check zhem!
http://community.modnation.com/en-us/players/IvoYaridovich/creations