Voyager!

Loved it growing up as a teenager and it was the first one I watched from start to finish. It has two of my favourite characters in all of Trek (Tuvok and 7of9) and my favourite captain (Janeway). The main downside is the lack of long story arcs (there's a two-parter called Year of Hell and a solo episode called The Void that both show off some off this missed potential); it's a shame they had to hit the reset button at the end of most episodes. Even then I absolutely devoured every episode when I watched the series for the first time.

Next is DS9. The Dominion War arc is excellent from start pretty much to finish... EXCEPT for the intervention of the 'wormhole gods', which felt like a cheap way to turn the tide of the war. Odo is one of my other favourite characters, and the show has some great recurring characters like Weyoun and Garak. The main downside? Too much religion, even casting the Captain as a religious messiah-like figure - ergh. Oh, and the fucking Bajorans.

TNG and ENT are pretty much tied for me. People forget how badly TNG started - it took a full two seasons before it found its feet and characters stopped acting like they were in TOS - and it has more than its fair share of dull episodes too (usually involving the doctor, Troi, or Wesley), but it was more rounded and had a better average success rate with episodes once you get past the first two seasons. Data is the stand-out character, of course. ENT also starts off slowly, in large part because it’s a prequel (stop doing this with Trek!) and was hindered by all manner of considerations because of that, but the Xindi arc is superb; possibly even better than the Dominion War arc in DS9. By then people had kind of given up on it, which is a shame, because the Xindi stuff is some of the best Trek ever written imo.

Then we move on from the great Treks to the Treks I don't really enjoy.

TOS has some good story-telling, helped in large part by the use of sci fi novelists being drafted to help out, but the technology and budgetary constraints of the time really show through; it makes it difficult to appreciate for someone my age. If I were a bit older maybe I could appreciate it more, but as it is I've never found the patience to watch the entire series. Nonetheless it has iconic characters (though I never liked Kirk), made great strides for sci fi on television, and gave us Spock, so for those reasons it’s my 5^th favourite.

Discovery. Let’s see, the good stuff: Saru is a good character and his race is pretty intriguing. It looks pretty, has nice effects, etc. I like Michelle Yeoh. The mirror universe makes an appearance. That’s about it. I dunno where to start with the bad, because it’s a very… messy series. It’s not really Trek, but if you just accept that and think of it as a non-Trek sci fi show then you’ll probably enjoy it more.

Still, I could quite easily kill off half the crew and the show would improve, rather than get worse:

• Burnham – good actress, but I don’t like the character, which was insubordinate so many times within the first episode that it's a joke she's still in uniform.
• Stamets – terrible actor and character. Just terrible, completely unlikable.
• Tilly – annoying character that’d never make it anywhere close to a starship, let alone COMMAND TRAINING ahahaha
• Hugh – bland nothingness, just there to be Stamets’ love interest so that they can have a gay couple, which is tedious pandering that I find to be patronising. If he had other qualities it'd be fine; then it's just a character who just so happens to be gay. But he's literally just 'that guy who for some inexplicable reason finds the utterly repulsive Stamets attractive'.

Picard. Oh boy, where to start. It’s so…. dull, and pointless. The writing is bad. The series leans on the crutch of bringing back beloved characters, but *SPOILERS* then kills half of them off (Hugh, Data, Icheb), or mangles their characters into unrecognizability (7of9 - thanks for butching my favourite Trek character guys!). The new characters are almost all unlikable. It manages, amazingly, to be even more overtly politically and culturally campaigning than Discovery, which means it will not age well. And while we’re on the subject of age, Patrick Stewart really is too old to be doing all the stuff his character does. I know they touch on this, and his character is frail, but that just emphasises the unbelievability of it all.

I did a full rewatch of all of the older series from late last year till June this year, so this one is easy for me. My personal ranking: 

1. Voyager- Unpopular opinion I know, but I've always liked Voyager best, ever since I was a kid. Great cast of characters (there isn't a single main character that I don't like, though Kes is probably the weakest of the bunch, trading her in for 7 of 9 was the best decision they could have made), interesting setting, love the heavy focus on the Borg, best set designs, best uniform design of all the series (DS9 only used it for the first 2 seasons before they switched to the TNG movie uniforms)
2. DS9- I did not like DS9 much at all when I was younger, but as an adult it speaks to me so much more now. Alot of the characters that I didn't like originally have grown on me over time, like Bashir and Quark. Love the heavy focus on religion/faith vs science, and the focus on war, neither of which is seen much in other Trek series.
3. TNG- Most people's favorite I suspect, I personally find it a bit overrated though. First 2 seasons were a bit of a slog to get through on my recent rewatch, there was too much TOS influence in those 2 seasons which really dragged it down. Gets better on the later seasons due to less influence from Roddenberry. I like most of the TNG characters, but TNG imo has the 2 worst Doctors of all the series, Crusher and Polaski, one of which was insufferably boring while the other was a poor copy of McCoy.
4. Enterprise- Very underrated show. First 2 seasons were a bit hit and miss, but the show got way better on 3rd season with the Xindi arc and stayed good on season 4, but sadly the first 2 seasons had already done their damage and caused the show to bleed too many viewers, so the show was cancelled before it got the full 7 seasons it deserved. Mostly good characters, not a big fan of Phlox though (3rd worst Doctor after Crusher and Polaski), and Hoshi and Travis were hit and miss at times, but I liked the rest of them.
5. TOS- By the time I was born TOS was already quite old and dated, and it has only got older and more dated since then. I was just never able to get into it, everything from the design, to the effects, to the acting feels corny and dated to me. I like most of the TOS movies, aside from the 1st one, with Star Trek 4 being my overall favorite Star Trek movie (followed closely by First Contact), but the TOS show just isn't for me. 
6. Discovery- Saw one episode of it and absolutely hated it. Visual design is horribly inconsistent with the other series, characters are terrible, plots are terrible. CBS locking it (and Picard) behind a paywall in the US also leaves a very sour taste in my mouth.

Haven't watched Picard yet, not sure if I ever will to be honest, as I have trouble believing that the same CBS that made Discovery actually was able to make a worthy successor to TNG era Trek. The writers on The Orville seem to understand TNG era Trek fans better than CBS and their writers do. 

Season 3 is coming sometime. Was supposed to release this year, but filming got halted in March due to Covid, and only recently continued, so might not release until early 2021. Fox sold the rights to Hulu though, so season 3 will be exclusive to Hulu. 

Huh?  Seemed pretty straight forward to me.

It's still in production.  But they moved to Hulu and then got delayed by the pandemic.

I saw the first season of Enterprise as a kid and didn't like it at all; I recently decided to give it another chance recently and I'm now partway through Season 2; it's not as bad as I remember and I think it is starting to grow on me.

The good thing about Enterprise is, it just keeps getting better. I started slow and ended practically binge watching the final season.

That's good to hear. It is very slow early on and the first season was definitely a slog, but everyone tells me season 3 and 4 are awesome.