I really think TOS MU is the best MU ever. I'm not that keen on ENT's though with rewatches I've liked it more and more. However the opening is just wonderful. The FC, the music (how GOOD is the music!!), it's an absolute treat. And who can forget the first time you saw the whole opening! Jaw on floor stuff. I remember being incredibly excited, very fresh for Star Trek.
Oh and I still like ENT's MU better than DS9's.