Bill Cosby has been pushing JELL-O products for decades ... and yesterday in New York the living legend finally told the people what they wanna know ... his favorite flavor.

Cosby was cruising around Midtown when Bill revealed which JELL-O product makes his taste buds go zip zop zoobity bop.

So did Bill pick Tapioca? Chocolate? Grape?

Guess you'll have to watch the video to find out.