T-Shirt: 50% (all with a pocket now--for reading glasses)
"Polo": (3-button Henley) 40%
Long-sleeve T: 40%
3-Button Henley (long sleeve): 20%
Flannel button-up: 40%
I have a hard time finding casual cotton button-down shirts with plackets that don't pucker up after washing. Some 100% cotton shirts do fine, most have plackets that need ironing after a few washes--I don't wear those much after that starts happening.
"Freedom begins when you tell Mrs. Grundy to go fly a kite." - R. Heinlein