Babylon 5 is by far my favourite science fiction experience. I've rebought the box set and hope to do a rewatch some time this year.
Farscape. I don't think that there has ever been a series quite like this one. Brilliant story with some of the best characters to grace the small screen. I did hear somewhen that there was going to be another series. I really hope that this is true.
Battlestar Galactica. The old series for nostalgia, but Ronald D. Moore's reboot was just sublime.
Firefly. I got into this late and wondered what all the fuss was about. I watched it in one sitting and i knew what all the fuss was about. Possibly the best first series of anything, ever. I thought Serenity was a bit lacklustre, though.
New Who. I bing watched this at the start of lockdown. Very good with some great stories. A lot of great companions, too. I stopped halfway through Peter Capaldi's Doctor and need to return to it.
Red Dwarf. Hilarious with some great science fiction stories.
I'd probably add Killjoys in as a personal favourite as i really enjoyed what i saw of it and should go back and finish it. Great fun with some very likeable characters.