Olfa is by far my favorite. If you have a Joann's near you, you can usually catch a good sale with a coupon. I purchased a 30 x 72 with a 60% coupon and love it. It covers my dining room table (my dining room has become my sewing studio).
Right now I'm doing a lot of small cutting (foundation paper piecing) and have put a smaller mat on top of where I always sit and cut so I won't wear the matt out in one spot.
I have a 17 x 24 (or so) version of Alex Anderson's quilter's select. And since I didn't start on it, I have a hard time getting use to the slickness of it. It pairs nicely with her rulers which stick to the fabric more. I just don't use it much.