These two are the same idea at two price points, so I would not agonise over the rubric here - they land within a rounding error of each other, and the R9 V3 noses ahead on paper because its software and ecosystem axes are a touch more mature. What the numbers do not show is the torque. The R12 V2 gives you 12 Nm against the R9's 9, and once you are running heavy FFB in something like iRacing that headroom is the difference between forces that clip at the top and forces that keep climbing. On the R12 you feel every bump and the kerbs stay crisp right up to the point where a 9 Nm base would have run out of room.
For $100 / ~£80 the R12 V2 is the one I would point most people at, and not only for the extra grunt. Twelve Nm sits in a properly useful spot - enough to feel like a proper direct drive without needing a bolted-down rig to survive it - and the R12 was the base that made the rest of the mid tier sit up when it landed. The R9 V3 is no slouch though. It proved that 9 Nm and PC-only could go toe to toe with Fanatec on price and win on the upgrade ladder, and at $299 it is the cheapest sensible way into the MOZA world.
So the split is simple: if money is tight, or you are new to direct drive and not sure how much torque you want, the R9 V3 gets you in the door and leaves the ladder open above you. If you already know you like your FFB strong, or you just want to buy once and not think about torque again for a few years, spend the extra $100 on the R12 V2. Both share the same MOZA Pit House software and the same upgrade path, so neither is a dead end.