From my experience:
Allentown is #1 period. People come there to spend money.
Expo is #2: meet lots of serious pinheads and good relationships developed
TPF: is so so, probably will not sell a ton but there is lots of foot traffic. The problem with TPF is the money you have to spend as a vendor to get there, stay there, setup there and then it is almost impossible to make your money back at this show.
Southern Fried Game Expo: by far the worst show for a vendor. Horrible