You guys act like windows phone doesn't lag at all. Now that's not to say android doesn't lag, it certainly does, but windows phone does too. In fact every os lags e even iOS.
And yes. The S4 had a lag issue because of the amount of features that Samsung forced on there.
True, all OS's lag, but if it was well build with the hardware it wont, the case for WP and iOS to lag is really rare. I've had my L920 for 5 months and I can assure you that I haven't experienced a second of lag (with abt 120 apps and games installed). haven't tried iOS.
But also and don't get me wrong my Lumia 920 with two cores compared to my(was) Samsung galaxy S4 with 8 cores and double the ram, the s4 still lagged. I think people should blame android oems and not android.
Its like Windows OS (desktop), PCs with too many oem software preinstalled will have a chance to lag more than PCs with fresh install of windows. there is a research for this info.