I've had rapid fire since I started biking, so I like rapid fire. I tried the dual control and I just didn't like it very much. I definitely prefer the independant levers. I haven't really tried the grip shift, other than the occasional ride on the road with DH bike. My Dh, on the otherhand, has ridden both and swears by gripshift. He absolutely loves it. He traded his SRAM XO rapids for gripshift (rapids being worth more) because he just loves the gripshift.

Basically, I think it's personal preference. If you're lbs thinks you should try gripshift and you haven't tried them, ask if they have a bike you can take off road to see if you like it