to my ear, D'Addario XLs sound like somebody banging pots and pans together, an unpleasant clanging. their windings feel particularly coarse and uncomfortable to me; they tear up my fingers like i was playing a round file (and i play a lot - i have pretty good callouses). i prefer a string with a smaller diameter outer wrap and a sound more like a "zhing" rather than a "DING". i'm sure lots of people love these strings, but they're not for me.
Cons - new sound wears off quickly, tension balance from string to string.
I have been using XL170-6's since the late 90's. They are available almost everywhere and I know exactly what to expect when I put them on an instrument.
These strings have great growl, are fairly flexible, and have a nice tone when old.
They definitely have their own flavor. The highs are a little zingy when new, but settle down nicely. The mids are clear with a definite favor of the low mids. The lows are tight and controlled with an almost flat wound envelope to the open notes in the low strings.
If you are looking for strings and don't know what to try, I would say these are the perfect strings to start as they seem to be right in the middle of the tonal spectrum.