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.
I chose D'Addario flatwounds when I got my first 5 string. After years of using a well-known English brand (rhymes with photo hound) these strings were an eye opener. Some brands, the low B flopped around in the breeze. D'Addario utilizes various tensions to maintain playability throughout the finger board. I recently replaced a set after 3 years with some regret. They were just getting broken in.
Pros - They last a bit longer than other nickel strings, great sound out of the box, do not sound too bad when dead, VERY VERY VERY easy to play, well rounded tone
Cons - none really
These strings are killer. They have a cool contoured sound out of the box, but when they begin to die out, they develop an odd mid-range sound that some might find enjoyable. They are really good strings and are always a great fallback when your true favorite set just isn't available at the time (especially since these strings have been on the shelves of literally every music store I've walked into). The life isn't too bad either. They sounded great for a good month in my experiences which is longer than some of the stainless steel strings I've used COUGH COUGH Rotosound COUGH COUGH. Definitely give these a shot some time!