first you would need to consider location - if you are in americas the volla phones only have certain cell bands (for me that makes att unusable, and tmobile 2g only)
right now i think pro1x is currently a less complete port, certain things need work, keyboard slide detection, and right now you need to install manually without installer.
pro1x
+keyboard
+no notch
+/- side fingerprint (user prefrence if good or not, i tend to hit it accidently, is placed more for lefft handed use)
-still in progress, manual install
volla 22
+preinstalled
+volla seems very intent on making the ut experience a great one, includes custom info in the user manual
+seems like a solid port from my testing
-notch