I used Elixers for the last couple years but have just switched over Memphis Electric strings for all my 6 strings. I do use the nylon Rotosounds on my bass.
I agree the Elixer do last a longer but the extra treble you get from them is not necessarily a good thing. I use different gauges on 16 guitars and find that the Memphis strings add to the harmonics with out giving you all the extra treble the Elixers do.