I have had experience with a few ssk out there, either personally or friends. (UUC, B&M, Factory Z4/Z3, and recently ebay one)
All of them work to a good degree but what you're paying for is really the feel.
In the ranking, I would rate UUC and B&M in one class and all others in another class. Of course with ebay versions, it's always a gamble on fitment, quality, reliability, etc.
If it wasn't the fact that I wanted to stay with the whole "OEM" theme on my car and if I didn't have my old M3 shifter laying around, I would've installed the B&M as that comes very close to the UUC at a fraction of the price. Materials are top notch and you can definitely tell it is very robust based on the weight, movement, tolerance, materials.
Edit: if you plan on going the OEM route, pick one that feels best to you. Some of the shorter throws are more notchy and I know some people don't like the notchy feeling. In all honesty, the short throw distance between most of the OEM upgraded shifters are negligible at best.