in terms of being motion accurate the PSmove is a lot better than the wiimote plus.
but again, as a gun the PSmove sucks.
so as a replacement, the wiimote is better than the PSmove but not as good as a lightgun..
In my experience I've tried several PSmove's, cameras, distance and ambient light.
and it just get uncalibrated after some minutes.
they are ok for the most people since they work as pointing device with a cursor
on the screen, so you can get used to it. just like a mouse.
the problem is they don't work as an aiming device like a real lightgun. (what I'm used to)
lightguns doesn't need a cursor on screen and it always points to the right point of the screen no matter how long you play or move away from the position you were standing at the moment of "some" calibration.
Lightguns are really good at what they do, but since CRT TV are dead they a dead too. Sad
aside that some people claims the PSmove works better than a real wiimote plus on dolphin.
but I've never tried.