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.