Unpopular opinion:
Voyager is actually the best Trek series. Hear me out. I’m going to use a comparison to TNG because TNG seems to be considered best by many (not all, of course). I think that Voyager represents a slightly better version of TNG. We have an interesting premise, a strong captain, and some great characters. Now, you can argue that Voyager had some missteps, such as the useless Harry Kim, but what Trek series doesn’t? They all have some character or another that is poorly developed, they all rely heavily on technobabble to explain things away, and they all have some stinker episodes. Voyager does suffer from the same flaws that seem to plague all Trek series.
However, what allows Voyager to stand above the others is that it doesn’t take itself so seriously. It’s flaws are more easily forgiven because it never claimed to be perfect in the first place. When TNG has poor episodes the impact is more strongly felt, perhaps because TNG is held up as this idealistic representation of future society, delving into serious considerations of philosophy and politics. When it falters, it feels disappointing and a bit embarrassing. When Voyager falters, it feels like more like they were trying something new and maybe a bit silly and it just didn’t work out this time. I can appreciate the willingness by the writers to take Trek into more humorous, light-hearted territory, and I think that Kate Mulgrew played this perfectly (as we can also see in her portrayal of Red in Orange is the New Black; she balances drama and comedy really well).
DS9, Enterprise, and Discovery are great in their own ways, but also suffer from taking themselves a bit too seriously. TOS is almost in a category of its own, so I find it hard to compare against the more recent series', but it has other flaws that push it lower on the list than Voyager. I also noticed, while doing a whole watch of Voyager recently, that the highs are really high. By that I mean, the good episodes stand out as really good, some of the best Trek ever. I think people focus too much on the lows, and don’t give the series the credit it deserves.