For new quilters: the Olfa rotary mat. The rotary cutter you use depends on how they feel in your hand. some are heavy and some are light. Personally I prefer the Olfa rotary cutter where the blade automatically goes in to protective/carry mode when not in use; you have to squeeze the handle to get the blade out and cut. I suggest this one as there is less accidental cutting of yourself or someone else while working.
Once you have made quilting your passion I have different preferences. The Martelli mat. It seems to preserve the blades so they last longer.
ali