Definitely ENT. As I written more than once, I discovered ENT for me for only ca. two years. And I watched again and again and I am still doing it regularly and enjoying. I think, if ENT aired today, except some CGI it could be still called a good show.
VOY is my least favorite ST show of all times, while two main reasons: as a female I did not like the first female captain must be a psycho with Mickey Mouse voice, and as an engineer I did not like their endless resources and self-repairing ship, it made whole show unbelievable. I say "did not like" while, "hate" is reserved for the real life issues like murders, rapes etc. Until VOY, every single ST show (TOS, TNG, DS9) was the bench mark for sci-fi shows of their times: they are all something new for their eras and they have a message, if you like it or not. VOY does not fulfill both criteria. All characters (except 7 and the doctor and even they are not always more dimensional) sooo boring, cliche and shallow for me. Each time when we get the short trailer of next week, I could tell how the characters react, what kind of decision makes Janeway. Mostly I got right, no surprise, no mystery, nothing sophisticated, nothing I could learn/realize for the first time about humanity or myself. No constantly character development, kind of schizophrenia is a common character specification of whole crew. As a young person, I watched the VOY, since we always watched the ST, kind of casual act, nothing with passion.
ENT is a -so to say- kind of avant la lettre for the sci-fi shows. They did it before prequels became a mode. Probably, I like it too much, while I did not watch it as they aired and I was not handicapped and tired from the old shows.
Last year we made a ST rally, since we thought it would be appropriate for getting warm before I visit first time a Trek Con. I have to say TAS made me not easy, but VOY was really really torment. Maybe, if I did not watch whole the series in two weeks, I would have never realized that they are so bad. If I could use the energy of my fidgeting right leg, I could produce enough electricity for a year.

So I need at least a decade to try it again with VOY.