It depends what's important to you and if you are looking for the best value. My rankings:

Service / Ease / Elegance (soft product): Singapore > Emirates > Ethiad

Seat / Plane (hard product): Emirates > Ethiad (if new biz class product) > Singapore

Value: Ethiad > Emirates > Singapore (Ethiad business class fares tend to be cheaper and a better deal then Emirates or SQ)

Also, I would check out Turkish and CX as other options. TK flies SFO-IST-BOM and their biz class is quite nice.