I concur with the HK P7 trigger as being the best striker-fired trigger around. The OP asked for which was the best polymer striker-fired gun (assuming the gun's frame polymer, which rules out the P7). In which case, I'd have to cast my vote with the Springfield XD--of the various striker-fired polymer pistols I've handled (Ruger SR-9, S&W SW9VE, 2nd-gen Glock 21, 3rd-gen Glock 17, 3rd-gen Glock 23, XD-45 Service) I like the XD's trigger the best--smoother than a glock trigger, lighter than the Sigma's trigger.