Replying since you might not get much response...
I haven't bought one, but just settled on the Trendnet TU-S9 (Trendnet uses a Prolific chip).
From my research, the big players are Trendnet, Keyspan, and Belkin.
My application is programming CNC machine controls (Fadal, Fanuc, etc.) from a VM. I was planning to give the Trendnet a try first but didn't end up needing it (deal fell through on the new machine).