I think each horse is different--I've ridden horses in bits, and in hackamores. I even rode a horse who couldn't have a bit in his mouth because he had chronically inflamed gums which made him super-sensitive. I ride my gelding, an OTTB, in a hackamore because it was just too much of a fight to get a bit in his mouth. He was very stiff with a bit in his mouth, especially in his head/neck range but with a hackamore he's much more fluid.
But before I tried him in the hackamore, I did give the plain snaffle a pretty honest try.