The gauges are thick because the nylon has very low mass and does not significantly, if at all, contribute to the tension. OK. Here goes. These are my observations. YMMV:
D'Addarios sound like well-broken in rounds with a little less articulation, and the E string is a little looser; tension-wise, they feel a lot like a conventional set of round 40's.
La Bella blacks are dark and round but have good sustain. Tension-wise, the lights feel like the D'Addarios, the regulars feel like a conventional set of 45's.
La Bella whites are bright with the edge off.
La Bella coppers have more mids.
Fenders sound fairly bright, with good medium-light tension.
GHS are wrapped brite flats and have a little bit of rock-a-billy twang to them. They don't feel balanced to me, with the D and A having more tension.
Rotosound are big, round, dark and thumpy, designed to emulate a double bass with guts, both sound and tension-wise.