I was just in JoAnns on Sunday and the lady at the cutting counter was telling another customer to buy an Olfa cutting mat. She said she wasn't a quilter, but she heard they were great. I told her that pretty much all the mats at JoAnns were going to give her about the same performance. It was the rotary cutter that would matter most.
I actually bought a fiskar mat two months ago because it fit my table better. I liked the color better as well. :)
I bought a small Olfa one a few months ago and it warped. I have it sitting flat on my table by a window (that is always shut), but it is winter and there is no way it got hot or cold enough to do that. My Olfa (which is about 15 yrs. old) was sitting there too and did not. I figured it was something I did, or didn't do, not the mat's fault, but now I am not so sure.