U1MB is nice, but can cause video interference in some machines. More likely if you have something hooked onto the ECI/PBI. I was never able to get a U1MB to perform without video interference in NTSC 130XE's. (I gave up long ago.) U1MB has some nice feature not present in Antonia thanks mainly to Flashjazzcat.
As mentioned, Antonia has 65816 cpu. Could cause incompatibility with some games. (?) I've yet to see any issues with that, but hard-core gamers might chime in. There is a 65816 OS and a 65816 BASIC interpreter. It allows limited operations with the linear ram. There is a 65816 Assembler and provides access to Antonia's linear ram, also. Antonia is very easy to install, and I have found no video interference.
In hindsight, this would be an easy decision for me in favor of Antonia. But don't know if they are still being sold. Both would be a good choice, if you care to spend the extra money.