what is the most useful (for you) size charm squares, 4", 3", 2", 1.5" or some other size?

It depends what I am planning to make, but I really like the larger ones because you can do so many things. I was in a swap of 6" squares and I really them.

I'm with Sadiemae.

I have fun with 5" CP's.. there a lot of patterns out there utilizing them

I like either 4 or 5 inch charms. For me the 4 inch work better if I'm leaving them whole and I like the 5 inch for things like the D9P where they're cut to make smaller pieces.

I use all of them, I just prefer the larger charms to make a larger top.

I use all of them but I don't like it if you buy one and the size of the squares aren't the same.

5". I only collect one size so that I can combine them as desired.

gosh i feel dumb...i thought charm squares were always 5"

Well now I feel dumb because I thought the same thing.