I haven't tried all the names mentioned here, but of the ones I have used, my favorite is Transition. One of the main attractions of Transition is the engineers there will happily advise you on your mixdown.. what areas of the mix need improving, suggestions on what to try in the future, etc. You can learn so much just by being there. Jason at Transition basically taught several leading dubstep boys how to mix their tracks. Like all studios, some days are better than others, but when they're on it they blow most of the competition out the water. Simon at the Exchange holds it down too. Especially if your mix is tight to start off with, but i don't think they cut dubs.
As for "everlasting" dubs.. they will not last forever. They're far less susceptable to crackle, but the treble wears out dissapointingly quickly, and the sound isn't as deep, as loud or as tough as acetate. And I don't want to point fingers, but there's a growing number of cheap mastering studios who really don't know what they're doing. The cheaper options are, generally, worth avoiding. The dubstudio does seem to have a lot of happy clients tho
One more thing, it is worth taking your track to Transition (or any serious cutting house) to be mastered for a digital dub... i.e. a wav for playing off laptop/cd. The mastering process will utterly transform your track, and fundamentally, an unmastered track
is an unfinished one. The vinyl/acetate sound is just the icing on top.