My first mat was the Olfa 18x24. It works fine for smaller things, and I've made due for bigger things, but it was sometimes difficult. I keep it out on my sewing table and use it if I have to trim something up, cut up something small, etc.
A few months ago, I bought the 24x36 and it is so much better! It makes life a lot easier. You do need to think about where you are going to cut, and will the table hold the mat. Or some people cut on the floor. My 24x36 fits great on the island in my kitchen and since that is counter height, it saves your back. I clear off the island, put down my mat, and can cut my fabric while the kids are playing around me, and still be able to keep an eye on them, etc.
Wish I'd bought it sooner! But the little one is nice for small things because I keep it out all the time and it just sits next to my sewing machine.
