Of the series, all of which have their stand-out visual look one way or another, the sets that tand out to me as looking the most like they might be a functional starship are those of the NX-01 enterprise from Star Trek: Enterprise
. They're a little claustrophobic and there are concessions to functionality all over the place, befitting an operation piece of machinery, and the reletively early setting of the show. there are hand-holds, and places where you've got to duck you're head (even in the CO's ready rooom).
The sets for the movie Enterprise as they appeared in Star Trek: The Motion Picture
are a close second. Though, they appear more "movie set" in each following film.