Elixir Nanowebs are a perfect match of tone, playability and longevity. They do maintain their tone last at least twice as long as regular strings. And you don't have to put up with the squeaking noises that plague regular strings.
A couple of years back Elixir had a quality problem in manufacturing. Their strings, while sounding fine, tended to break very easily. The guitar playing community complained loudly, but Elixir seemed to dodge the issue. I nearly gave up on them.
But they did improve their materials without making any fuss over the issue. I would have preferred if they had acknowledged the input of the community but main thing is that now Elixirs don't break any easier than the competition.
I use nothing else now.