DS9
TNG
VOY
[a country mile]
TOS
[several million parasecs]
ENT
DS9 is easily the best of what the franchise has to offer, and TNG is what TOS wanted to be but was much better at it. VOY...didn't use its unique station as often as it could and should have, but was decent ultimately, despite some disappointments. TOS has its moments of greatness and does have some genuinely very good episodes, but overall it's not that great. ENT is like...I guess I'd choose it above torture. Well, maybe, depending on the type of torture.