USB and PCI/PCIe are on par due to interface design (FPGA doing USB I/O, not by 3rd party chip) and RME's excellent drivers.
You might have a little advantage by using devices supported by the MADIface driver, because there you can set 32 samples ASIO buffersize (instead of 48 samples with the "old" USB ASIO driver). But this is not a big difference.
In the blog article about the UFX+ I posted a picture of RTL (round trip latencies) of different RME solution that I was using.
You will notice, no big difference:
https://www.tonstudio-forum.de/attachme … es-v2-jpg/
I would focus more on other things
- the format of the interface
- only Babyface Pro FS supports to be powered by USB (PSU is an option)
- amount and type of I/O ports
- special features of the device like e.g.: DURec, Autoset
- amount of ADAT ports, if you need double speed (88.2/96 kHz) then you need 2x ADAT I/O for adding an external 8-Port preamp or AD/DA converter
- whether you want preamps with up to 75 dB gain range, then you need an UCX II, UFX II or an UFX+ (-successor)
- whether you need other digital ports like AES, MIDI, MADI
- whether you want a display for stand-alone operation (UCX II, UFX II, UFX+ (-successor)
- recallable config profiles for stand-alone operation (UCX II, UFX II, UFX+ (-successor)
Do not buy too small, having a little port reserve might be useful for you in the future.
For an easier comparison of available USB-/FW-based interfaces, you can use the following Excel sheet from my blog:
https://www.tonstudio-forum.de/blog/Ent … B-MADIfac/
Direct Link to Excel: https://www.tonstudio-forum.de/attachme … 9-19-xlsx/
UFX+, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1650v4, Win10Pro22H2, Cub12Pro