The first rulers I purchased were 6x24 and 12.5 square and that was a very long time ago...actually I had one before those that is 2x18 and not for rotary cutter use. If I could only have two rulers now, I'd have to check with my bee sisters to make sure we all chose different sizes to insure access to more of the many sizes that are available...how's that for teamwork? LOL Okay, just two? I'd go with the 6x24 and the 12.5...but I'd be trying every trick in the book to sneak in at least two more for sure!