There is a quality difference, but not in the way it may matter. As mentioned, the life of the pot is one thing and the smoothness or feel is another. The tolerance to me is not much of a quality thing. The pots are made and the manufacturer provides a tolerance. 99% of the pots that are sold will be within that tolerance spec. Whether you can hear the difference between a 500k and a 460k pot is the big Q mark. I can certainly hear the difference between a 250k and a 500k pot, but I don't think I could sit there in a blind test and hear a 50k difference either way with either pot. I have trained ears, slightly above average hearing ( for my age ), and am an audio engineer, so if I don't hear an appreciable change, then it is really not worth fretting about.
Now, where I do feel makes the quality of a pot more evident is the taper consistency. Most pots taper really smoothly and well enough for about 2/3rds of their sweep. It is the last little 1/3rd between 0 and 3 that is where the quality can really be noticed. Some pots have an abrupt cutoff or a rough and unpredictable taper that just makes using that last 1/3rd very cumbersome. Not many guitarists use that portion of the pot though. To mute the guitar many will turn the dial to zero, but for most guitarists, the zone from full-on down to around what would be 3 on the dial is about all this is really used.
I use CTS pots for my guitar and amp builds, as I find them to be the smoothest you can get over the entire sweep of the pot. For amplifiers, that first 1/3rd of the pot between 0 and 3 is the most important area, and Alpha pots for me seemed to have an issue in that realm. CTS on the other hand is great all around. Probably a little stiff for most guitarists, as they seem to use some thicker grease, which is probably why Alpha is more popular for guitar use, the pots turn easily and smoothly enough. I actually use the whole range of the pot because I prefer linear taper pots for my volume controls in guitars.
Linear vs. Audio taper..... I like linear taper because it allows for larger resolution between full-on and dialed back a bit. You have to use roughly 3/4 of the pot to get the same volume change as an Audio taper pot does in 1/3rd of its rotation. With a linear pot, the last little 1/4th of rotation works just as an Audio taper pot would when it is full-on. I like the resolution ( ability to dial in precisely ) linear taper pots have when used as an actual volume control. There are some Audio taper pots that are not as aggressive in taper and work really well, but I have not been able to source them and it seems to be a crap shot. YMMV of course. For me, I like linear taper because I know it will do what I want every time.
On a sidenote I've had the best experience with the SD branded pots: each one was within +/-3% of the nominal value, while the others were all over the place, usually below 500k.
