I just did a google search, found an internet forum post from 2007 that said they were going to stop making them. Since it is now 2016, good luck finding some new old stock.
I suspect that the demise of square taper is the reason for discontinuing. I am still using square taper on every bike, except a couple 40 year old bikes. I have no plans to change to a different system. But Shimano and most other component manufacturers don't like investing in top quality components of what they consider a dated design when they want to sell a newer design instead.
I am using UN55 on my Nomad, but I probably have less than 10k miles on that bike, so not a hard test yet.
Most of my derailleur bikes (including Sherpa) have Campy since I am running Campy cranks and they have a slightly different taper than Shimano. So, my Shimano bottom bracket experience is quite limited.
I have seen good comments on SKF on the internet, but do not have first hand experience. At that price, they better be good.
A friend speaks highly of his Phil, but I think he is buying cheaper bottom brackets for new builds.
I do not know if Velo Orange is considered a good one or not, but some of their stuff is quite good.
http://store.velo-orange.com/index.php/grand-cru-bottom-brackets-hollow-axle-alloy-cups.htmlI bought a used cup and cone bottom bracket, if my existing UN55 goes out, I plan to switch to the cup and cone. But, some of the spindle bearing surfaces are pitted, so that experiment might not last long. After that, I will probably just stay with UN55, but if I suddenly get an urge to spend money then maybe the Velo Orange.