This is a hard question, it is all about personal preference. I have several different cutters, but my favorite is my Fiskars rotary cutter that has a button by your thumb that releases the blade back to the safe position. I have both Fiskars and Olfa cutting mats and like them both. I had to replace my6x12 ruler and bought one of the frosted ones, and I really like it.
What I don't like, June Taylor cutting mats...too much like hard plastic.
For mats the better question might be what size. My suggestion is, if you have the space, go with a larger one. But, remember they must be stored flat--some people store them by hanging them up using skirt or pant hangers (the clippy kind).
Welcome and good luck. This was a really smart question.