I would be hard pressed to make a decision here.
But...
B5 first - but I never did get my head around the change of station commander - was that supposed to happen or just a casting issue?
Farscape second - dead sad, sudden, and unexpected the way it ended.
DS9 third
Way down the field we have the rest of the star treks, Andromeda, star gate, etc etc
Ask me tomorrow and i'll probably put the big three in a different order.
PS: Haven't seen the new series of BSG yet. Looking forward to buying the DvDs at a discount store one day and watching the lot.
PPS: Reminds me - right at the bottom of the list, so far down the field you'd need a radio telescope to even see it I would have to put the original BSG series. With Buck Rogers (Erin Gray mmmm).