Awhile back I had quite a few builds where the shaft diameter (6.35mm shaft) needed to be fairly exact. The Alphas were far superior to the cheaper ones in that regard. I tried Cusack, Mammoth, Tayda, and ModularAddict pots, and they all had quite a bit more variation (50%+ of the shafts were too narrow for my use, Alphas were pretty much all perfect). That particular difference won't matter or be noticeable for most cases, it was a pretty minor difference. But it may point to tighter tolerances overall on the Alphas.
Personally, I tend to use Alpha just because they've been around long enough to have a good idea of how they will hold up over time. For personal projects, I'm not opposed to using some of the other pots. I haven't had any issues with them in the short term when I have. But I tend to stick with Alphas and if I was building anything to sell I'd definitely go with Alphas. Beyond the fact that Alphas are time-tested, I wouldn't be surprised if the generic pots some of these places sell (particularly Tayda) change without notice from time to time.