It's really an entirely different animal than either of them, but ranks right up there with them in terms of quality.
SG1 is a 50/50 serious/fun ratio, with long running plot threads mixed in with adventure- of-the-week episodes. It's a bunch of friends saving the galaxy and having fun doing it. It's got a real sense of Earth's slow progression from the mostly forgotten backwater homeworld of humanity all the way to being a major power in two galaxies.
B5 is like a 90% serious novel about war and politics.
BSG is 100% grim, and it becomes really obvious in later seasons that while the Cylons might've had a plan, the writers sure as shit didn't know what it was supposed to be. This unfortunately makes it overall the weakest of the three IMHO.
If you missed SG1, I am guessing you missed Farscape too. It really makes aliens actually Alien, it's universe is so weird and fantastic. And the characters and their interactions are great.
Definitely worth adding to the list.