Went to Rainbow today. The falafel was every bit as as delicious as promised--esp. that peppery hot sauce! Despite loving my sandwich, however, I still don't think Rainbow is in quite the same league as Azuri Cafe. Comparison is difficult because the styles of falafel are so different. But my criticisms were that the pita didn't stay together well, the falafels were pre-cooked, and there was nowhere near the variety of salads available. (Every sandwich or platter at Azuri comes with dollops of about 7 or 8 fresh and colorful salads.)
My feeling is that Azuri is still the best of the best in Manhattan (an important qualifier) while Rainbow remains the best of the rest (it's closest competitors being Alfanoose, Mamouns, and Hoomoos Asli). I give Rainbow the edge over the rest because of the tasty flavoring of the falafel and that absolutely divine hot sauce, which is quite unlike any I've ever tasted.
Still, I know there's bound to be dissent on this question. So let's hear it!