Reading this thread has made me wonder whether Rotosounds just don't travel too well - I've still yet to be let down by a set, but then I am buying them in the UK, and only about 30 miles from the factory at that!
I've not tried a massive range, but the biggest let-down for me have been Ernie Ball. They sound lovely when you first put them on, but if you pick up the same guitar/bass a couple of days later you wonder whether somebody came in and swapped them for an old set while you were sleeping!
The tone just seemed to die off too quickly the few times I've used them. I'm sure they're great if you can afford to change them every other day, but I certainly can't!