mushkin usually uses a mix of Infineon chips (for the REV 3 stuff and more expensive rev2) and mosel, IBM, Nanya, and Samsung for others..
All my mushkin is built with Infineon chips and i have had no complaints about it, it does what its supposed to do.
Again, this is 14th hand info, but Infineon is said to be a great O/C chip. But my experence in that arena is limited by a p3 that won't go above a 127mhz bus.
Other than that, i can't say much else....