I just downloaded nova. I like it but it takes away a few things the stock launcher had (that i found really handy). Maybe you can add the things back in, but I haven't figured out how to do it yet.
First, I am running Android 4.1,so this may not apply to your nexus... With the install and use of the nova launcher, I have lost the quick settings feature when scrolling to the extreme left of the home screen. I have lost my favorite apps page in the main app screen. Also, getting to the play store involves pressing two buttons instead of just one (in the top right hand corner of the app menu).
That aside, themes for the nova launcher need to be separately installed from the play store. I am personally running the HTC Sense theme on my RAZR HD and it is pretty nice. Nova also lets you implement some nice scrolling features on the home screen (such as cube and card stack).
Again, since i am a little over 24 hours into experimenting with this launcher, I am still in a learning curve.
Now I will say that I have tried GO launcher and was disappointed. I didn't like the feel or the detriment it gave to my phone (lost some great features the home screen had from the stock launcher) I also had GO SMS installed for a *very* short period of time, but I uninstalled that because it wouldn't let me send pictures without prompting the receiver to download the GO SMS app (and put the photo in a file that only the GO SMS app will open due to the attachment string). I won't say any more about GO SMS cause your post was asking about launchers...
Those are the two I have used although I am sure there are many others out there. As said before, try a bunch and form your own conclusions