I made the comment in this image that I would have a hard time deciding between the taur beast and the snake, if I was forced to make a choice of one to be... I think one thing I really like about the snake form is the verticality of it: The yuan'ti doesn't have to live his life on the ground at all, which would really open up spaces, almost as much as wings. In some ways, even more than wings: take a set of ruins like here; for a large winged creature, navigating them would be a challenge, but not for the noodle.

And, apparently, not everyone looks up when exploring ruins.