I have 2 Olfa mats. Both are about 25 years old and still going strong. I can't say the best place to buy - one was from Joann's when they were having a terrific sale. The other one I got in a starter quilting kit. I was told they last longer if you soak them in water from time to time. I did one, because it fit in the sink, I don't have a big enough place for the other one. I do have a white mat - believe it is from Dritz, not sure. A friend bought it because she uses her kitchen table, it was large, a great price, however storage was a problem for her so gave it to me.
You definitely want a self-healing mat, your blades last a LOT longer with them.