Genymotion is a fast emulator for android which can be used for development or for other android usage if you know the tricks of the trade!
Gm emulator uses android AOSP image & runs on virtual box using virtualisation. Since it uses visualisation it could use hardware acceleration features of the CPU and the genymotion AOSP images are optimised for the same, hence genymotion emulators are the fastest emulator for android i.e until android studio 2.0. Though latest android studio emulators work on similar fashion; which one of them is faster depends upon your use case. Anyways, flashing Google PlayStore on android studio emulator is more tricker.