Seriously, the smoothest launcher on Android is...
... TSF Shell. Goddamn.
I have had it for quite some time and was using it on and off because as awesome as it is I just don't find it as practical as something like Nova/Apex.
However, I started using it again yesterdat and I have not seen such smooth operation on an Android device anywhere else. Only my N7 pre-4.2 was this smooth. I am still not going back to it full-time but it shows how smooth Android can be with the right coding. It quite literally is iOS-smooth (a loaded declaration, I know, but I seriously believe it).