I have a 24x36, two smaller ones and an 18" rotary mat - all Olfas. I try to remember to use the smaller ones when possible, so I don't wear out the more expensive 24x36 mat. I would buy the largest one you have room for and also a rotary mat. I don't know how I ever got along without my rotary mat. Trimming blocks is so much easier when you can spin the mat instead of the block. Jo-Ann Fabrics and Hancock Fabrics both often run sales or have discount coupons.