what are the advantages?

I'm thinking of building a tadpole recumbent and was wondering on which drive type would be better.

I only know of one FWD tadpole trike commercially available, and that's the one by A.S Engineering (http://www.aha.ru/~ykpro/index.htm) . The reason is mechanical simplicity and drivetrain efficiency. By necessity, the ASE trike is shaft drive, and putting power to the steered, driven wheels causes more loss than a chain setup going to the rear wheel. Still, I've always been impressed with the ASE trike - it looks cool, and efficiency be d*mned but the shaft drive has a super-high zoot factor! (YMMV.)

come on folks - you must have some preference whether it's based on efficiency or personal taste.