I've always been partial to the Fleming version, because IMO it was a relatively harder quiz show, Fleming was a true gentleman all through Jeopardy's run (both of them), and the visual elements (set design) were modest yet effective for its time, though I always loved Jeopardy! '78's crimson and cream board and set, as well as its "odd" dollar amounts ($25, $50, $75, etc.).
Trebek's version was a little startling when I first saw it, but it grew on me rather quickly and I respected the show on its own merits, though the show's second set (light blue and off-white) took a while to get used to because it was so "bright". For the first 3-4 seasons, I watched it regularly if not religiously, then afterward occasionally due to my teen and young adult years taking place, and by the time I got to my college years, Jeopardy! was beginning to get too gimmicky and was turning into a caricature of itself, which turned me off from watching the show with any degree of regularity, though I did enjoy watching the Super Jeopardy! eps in the summer of 1990.
My vote is for Art, his hosting alone was in a class all by itself.