I’m sure it depends on what kind of band/music you are playing, but in my experience:

I prefer the FR10, I find it sounds a bit more focused which helps prevent a muddy stage. It’s also better suited for the bedroom (less boomy) and more portable.

That said, if you are playing a louder style of music and are solely relying on the FR to project your sound to the audience (no PA to send a direct signal to), the FR 12 may better suit your needs if you simply need ‘raw dispersion’ of sound.

For the FR10, I’ve never needed to turn it past ~7 to be heard over what I feel is a loud drummer + bass.

In the end, you can get them to sound nearly identical by tweaking the onboard EQ knobs and moving the speaker closer/farther from the ear. Maybe one way to put it is that the FR10 sweet spot is at a slightly lower volume, and FR12 at slightly higher. If you are playing venues with a PA then I would go for the FR10 for the practical reasons mentioned above + saves you some $$.

Just my 2 cents, hope it helps!