I watched all of Voyager, but to me it's still the worst Star Trek series. People have already named most of my reasons, so I won't repeat them. The real pity was that the premise and some characters on that show were amazing. The Doc is still one of my all time favourites. On the other hand, Neelix was just cringeworthy (and I don't use that word lightly) - awkward, unfunny and annoying. Overall a lot of wasted potential!
As for Enterprise - I actually liked it for a lot of its run! It fell off towards the end, but most of that series felt very solid to me. Some good characters, and the setting was fresh and interesting. Some good plots too. Could have been better, but I don't really get the hate that show has garnered.
And all that DS9 talk makes me want to rewatch it again. Such a good series! I agree that Dukat was a fantasic villain. IMO the best one Star Trek ever had. And the show was also bold enough to smack our beloved Starfleet heroes with some truly dark shit - "In the pale Moonlight" is still in my top 3 Star Trek episodes ever.