This is my experience on my Galaxy Nexus -- which is no hot performer anymore, believe me.
I prefered the options and features available in Apex over the ones available in Nova. It was only a few minor things that I probably could do without, but I've gotten used to it, so for that reason I use Apex. That being said, Nova does seem slightly faster and smoother then Apex does.
Now I can't tell you if either of them will be smoother/faster/better then the KitKat launcher, because I'm running a ROM -- the only way my Gnex remains stable enough for daily use (ugh)
Best way is to try Nova (free) for a few days, and then switch to Apex (free) for a few days. If you like one more then the other, believe me I find its worth a couple bucks for the full version which unlocks gestures and some other goodies (both for Apex Pro and Nova Prime).