The UCX II has the more complete feature set and also got some features of the flagship interfaces UFX II and III.
Autoset, DURec, Display, Mic Preamps with a gain range of 75 dB, full implementation of FX chip, stronger phone outputs.
It has WC (word clock), which you should have just in case you need to connect a preamp without digital input (to receive clock signal). More I/O ports and more variety in terms of types of ports. More analog I/O ports make it easier to integrate e.g., external FX, be it Lexicon PCM reverb unit or what not. Then also the new features Room EQ and Crossfeed.
https://forum.rme-audio.de/viewtopic.php?id=38691
The Babyface is designed to be a mobile interface which can also be operated with USB bus power.
Therefore, it has some limitations and not all features like UCX II or the flagship interfaces.
A disadvantage can be the cabling on the desk if you plug all cables on all three sided.
So if mobility is not your 1st priority or "must have", then the UCX II is the more complete offering port and feature wise.
You can use my Excel comparison sheet to compare the interfaces.
https://forum.rme-audio.de/viewtopic.php?id=35156
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14