My vote for best falafel in midtown has got to be the halal cart of the south-east corner of 52nd and 7th. It has become my mainstay for lunch. $4 for a falafel sandwhich can't be beat.
Also, they are very vegetarian friendly, making fresh falafel in the fryer when you order, not warming anything up on the flat top with the meat and using separate tongs for it all.
Anyone have any nominations? I am bit obsessed with falafel and would love to try some others.