I'd found THE STRING in the old Prisms, and was so p*ssed when I heard they were discontinued that I sent off a "strongly worded" e-mail to D'addario ("strongly worded" adult-like, as "You're going to loose a customer because of this", not "l33tly worded" like "im made and wil ne7er us3 u aga!n"

) I actually got a quick reply from their Senior Marketing Manager who offered to send me a set
gratis if only "to see what you hear to be the difference between Prisms and ProSteels."
Within a week I received a box containing a five-string set, a t-shirt, and one of their promo CDs. I strung a bass up, and needless to say I was right - they weren't as good as Prisms.
They were
better. Perhaps only by degrees, but I find them a bit tighter in the low-mids, a bit more "chime" on the high-end, and even longer lasting. I quickly sent a "swallowing my pride" e-mail back, and instead of throwing it in my face he thanks me for the comments and that they were able to keep me as a customer.
I use D'addarios exclusively, ProSteels on fretted, XLs on fretless, the occasional Chromes for the traditional flat sound, and might try EXPs one of these days to see how they compare to Elixirs for my fretless. I do so primarily because they contribute to "my" sound, but also because of their care for quality CS and QC as seen above. They haven't endorsed me (...yet

) but I happily endorse
them.