If I could only pick one and it were to be "locked in" for life - I'd have to go with Deep Space Nine.
I understand why people say Babylon 5, but for me it's a bit too "rough around the edges" to be an all time #1.
I could argue DS9 is a bit of a cheat answer due to it being Star Trek, however even if it were in a vacuum I think it'd still be my number one. There are just too many singular episodes that stand out with a great overarching storyline to boot.
SeaQuest unfortunately gets weird towards the end. But i loved it anyways. I thought Darwin was so damn cool lol.