Countertop height + or - depending on your height. I am tall so mine is countertop plus 2 inches. I often put whatever I'm mixing or dicing on a thick cutting board when I have to stand at my counter for long periods so the height of my custom cutting table was a no brainer for me.
I actually prefer my 36" square top cutting table to the larger ones. I can easily walk all the way around it to cut all angles. I can see where the larger sizes would be handy for squaring a quilt but I spend way more time cutting & sub-cutting strips for blocks & borders so the smaller size works better for me.