0. TNG. Most cerebral, most concerned with matters of ethics, great camaraderie between the characters (and actors, IIRC), most humanistic and hopeful.
Outside of Wesley (and even then, he was occasionally nicely written, as in The First Duty and Final Mission) and Tasha/Worf stepping on each other's toes in S1, all regular characters are pretty good, IMO.
I feel TNG had the best overall writing quality. A few dreadful episodes, but not many.
TNG was more mature than the others as well in that its villains were not cartoonishly evil "we're going to dstroy everything for destruction's sake" ones, they were rather more realistic: either fanatics (Admiral Satie, for instance) or self-interested sociopaths (e.g., the alien from Devil's Due).
None of that pah-wraith nonsense.
1. TOS. Ups and downs, but it went where nobody had gone before and the chemistry between the characters is just there. Too campy, hasn't aged great, but still fun to watch.
2. DS9. Although I dislike the pro-religious outlook (and the ridiculously medieval "prophets vs pah-wraith" dichotomy of the latter seasons) of the whole series, it had a few great episodes and some very good characters (Quark, Garak, early Dukat, Weyoun, Jadzia).
Sometimes, the interactions felt forced (usually when they involved Kira), but sometimes they clicked very well, like the O'Brien-Bashir friendship.
3. VOY. At its peak, VOY was very good, but it very rarely reached those peaks, and the camaraderie between the characters felt forced most of the time. In the end, most characters were either forgettable (Kim), neurotic (Janeway) or annoying (Paris, Torres, Chakotay).
Neelix deserves a mention on his own. Over the whole series; all but one scene with him were cringefests. The most annoying character in television history, eclipsing even Wesley.
Best theme, though.
4. ENT. Some good, but nothing great. Pretty mediocre overall. Most characters were bland, themes and allegories removed in favour of a continuous story high in adrenaline, but low in substance.
5. DSC. Forgetting the "Trek" part of Trek. At the moment, it's "Star Wars: the live action series".
Writing is often bad: excess exposition, a "tell, don't show" approach to characterisation, which leads to informed attributes for Mary Sue Burnham (at least SHOW her being "the bravest" or "the smartest", rather than merely have the other characters exclaim it), the motivation of the Klingons is unclear at best, clichés abound.
Character wise:
- Tilly could be a new Neelix. She's more at Wesley levels right now, but there's potential for worse.
- Tyler seems to be there solely as a romantic interest for Burnham.
- Lorca just isn't a good person, and neither is Burnham.
The only one I like is Saru. Captain Georgiou was ok, too, but well, didn't last long.
Morals? Not only are they no longer discussed, but quite frankly, the Federation of DSC does not seem to believe in them. Gone are the days where the Federation held itself to standards, even if it cost them dearly.