I would say the 3moa - at long distances the 10 would get in the way. Also, you'd have a hard time getting the 10 anyway - most people stocking them have the 3 moa (although the popularity may also tell you something).
I love it on a FAL - I don't have the best vision in my right eye (esp. through tilted down glasses) but with the red dot it's amazingly easy to just rapid-fire at the target, with both eyes open.
It's also a lot less work - while you may strain to get accurate hits with irons, you just relax both eyes and look dead ahead with the aimpoint - and let the trigger break when the dot covers the target. Also, it's easier to reacquire target quickly.
Battler.