Every time I get asked this the answer is different.
This time, I think... Enterprise.
Season 2 had some promising bits, despite being utterly bland otherwise, and Seasons 3 and 4 were neat changes of pace for Trek.
Personally, Voyager never really grabbed me. I mean, there's plenty of neat standalone episodes, but it felt very TNG. That isn't to say ENT didn't feel TNG at times, but it made efforts to depart from the TNG/VOY norm.
I would have liked to have given it a chance to have a fifth season, but on the other hand, I can't even bear VOY reruns.