Stargate SG-1 and Atlantis - got just the right amounts of science and fiction, drama and comedy, campiness and self-awareness, and is the reason I got interested in physics and programming. Undomesticated equines could not remove me from another rewatch.
Stargate was such huge part of my childhood! To this day I remember almost every episode of the original SG1. Atlantis ran on cable which we did not have, so the first time I saw it was later on in my adulthood. Sure, Star Wars, Star Trek, Expanse and BG are all great, but man, SG1 will always be my absolute fave.
Honorable mention goes to Farscape - what a ride that show was!
Yes! I loved Farscape, too, although I was able to only watch one season - but I'm planning to fix it soon. I just recently realized the reason I loved Guardians of the Galaxy so much, is because it reminded me of Farscape - mostly in costume design and team dynamics.
Another, modern show worth a mention, is Travelers, from the same creator as Stargate. Much more serious in tone, grim, even, but still extremely engaging.
I miss these series so much, and really wish they would've continued with SGU, but I think it was ill-fated due to the timing of the series. It was really getting it's legs in season 2.