I love both, although if forced to pick one at gunpoint, I'd say Babylon 5. It's worth watching at least twice, because some events that are set up during season 1 happen in season 4! Admittedly it's a bit slow to get going in season 1 as all the characters and their cultures are introduced. Sadly season 5 is a bit flawed. Don't get me wrong, I enjoy it more than most other shows on TV, but it feels tacked-on, which is only fair given that they thought the show would be canceled after the 4th season for the longest time, and were forced to compress events that were intended for the 5th season into the fourth. The fourth season finale is IMO rather blah (the show finale was shot as the last episode of the 4th season).