I started out using cotton mitts and am now trying out the MF mitt from CMA. My comments about both below:
Cotton Mitts
PROS: covers a big area, easy to grip because of flexibility (which makes it less prone to dropping), drys rather quickly
CONS: hard to find 100% cotton versions at local stores (most by me are cotton/synthetic blends), loses fibers fairly easily (longevity issue?)
MF Mitts
PROS: does not lose fibers easily, does not feel like my hand is getting as wet as when using the cotton mitt, seems to be easy on the car finish
CONS: covers a smaller area, harder to grip because it is not as flexible as a cotton mitt, unable to find locally (must mail order)
I have only used the MF mitt once, just this week. Unfortunately, midway through washing my car, it fell off my hand and onto the pavement. Call me a klutz, but I have never had a cotton mitt slip off my hand. I would like to try a MF mitt that has a built-in thumb. One last consideration that is totally subjective (like the rest of my comments): I wonder if the shorter fibers on the MF mitt make it less likely to retain dirt and debris than cotton mitts. I would like to know what my fellow Autopians think.