my experience with GenericUSBXHCI vs either PXHCD or the CalDigit kext is simple:
my probook doesn't have USB3, so i bought a "mac compatible" USB3 expresscard. there was no problem with the expresscard being recognized by OS X when i inserted it. with either PXHCD or CalDigit, System Information-->USB showed the expresscard's port as SuperSpeed, but with a speed of 480 mb/sec. testing confirmed that in fact it was operating at usb2 speed.
however, with the GenericUSBXHCI kext, the expresscard's port is recognized as SuperSpeed, with a speed of "up to 5GB/sec". and, testing supports that info.
also, i have a desktop hack with a pci-e usb3 card (NEC chip) that never worked properly with the older kexts, but does work fine with GenericUSBXHCI.
so, my strong vote is for GenericUSBXHCI in the installer.
ken