What's the most effective in your experience? I have them in lots of different brands and mostly they are a bit wrinkle resistant but far from being really effective.
I have one that is almost 100% perfect, its a Pierre Cardin "polycotton" shirt that can withstand the harshest spin dry without a crease - its way above all my others and shows what's possible, but I also have other Pierre Cardin shirts that dont work nearly as well. The term "polycotton" hides what is in the materials of the effective one.
Polycotton is a blend of polyester and cotton..
The best no-iron shirt that I have come across is a wife. :)