Which Star Trek series is your favorite?
The original, hands-down. Despite some ridiculous episodes (Spock's Brain being a prime example), it was the dynamic of the relationships between Kirk, Spock and McCoy that made it so immensely enjoyable to watch. Plus, the genius of Roddenberry to put mixed races and nationalities on the board of the ship (including putting a Russian and an African-American woman on the bridge in the middle of the Cold War and at the flashpoint of the Civil Rights movement), not to mention foreshadowing desktop computers, floppy disks and a whole host of other technological advances (though I'm still waiting for my transporter!). I have happy memories of discussing issues like the merits of the Prime Directive, changing history via time travel, etc., based upon episodes of the original series and I enjoy watching them to this very day.
DS9, even if it was a rip-off of Babylon 5.
I would have to go with DS9.
TNG a close second. Very close.
I never really watched the Original, it gets silly.
TNG, followed by Enterprise. Of course, I grew up on TOS, and will always like it. I did like Voyager and DS9.... but I got into DS9 much later and haven't seen a lot of it before Worf arrived. As for Discovery, I've seen only the first hour, so I can't say. I'll reserve judgement on that one.