I use 45 mm one almost all the time. I bought one of the new ones with ball bearings which was easier on the wrist, but it came loose after using for a while, and I had to re-tighten it. So I went back to my Fiskars one. I also have an Olfa 28 mm one that I use mostly for curves. It seems sharper but maybe that's just me. I have a small 6" x 8" mat that I use to cut borders when layin out my quilt on the ironing board, and for that I also use the 28mm cutter.