I've used the Fenders, the LaBellas, and the Rotosounds. That's more or less the order in which I liked them--Fenders slightly better than the Labellas, and quite a bit better than the Rotos. The 88s seemed fat and rubbery to me, in feel and sound. The LaBellas are slightly thinner, and though their sound is still pretty dark, to me they seem to produce better treble. The Fenders, a little more so.
To me, the Fender 9120s seemed the closest in feel and sound to regular strings. Also, the Fenders were the only ones that didn't require me to widen the nut slot for the E.
same opinion here.
plus, the labella and roto88 fills more rubber rough and muted with less sustain.
but the fenders are more sleek and have more sustain and wide sound.
maybe the labellas and roto are more reminding gut string and the fender are more like flat wound still strings with much less pressure.
