I have 4 regular ones:
12 x 18
19 x 25
25 x 37
36 x 57
2 cutting/ironing combos:
14 x 20
18 x 25
1 revolving:
12 x 12
I use most of them. The cutting/ironing combos tend to curve some, so I don't usually use them to cut, just for ironing, but if I go to a class I might take one just as a space saver.
The largest one 36 x 57 I keep on my counter 99% of the time, just as a great work surface. It doesn't seem to heal a well, so I don't like to use it as a serious cutting surface.
I only use the revolving one on occassion, but I am really glad I have it when I need it!
The 12x18 I keep next to the sewing machine.
The 19x25 and the 25x37 I love love love. One goes on the counter (where the really large one is all the time) the other moves all over the place.
When not in use, I keep the flat ones under my area rug in the family room.
Alice