I actually have both as of yesterday. Prime is great for video, comics, email and just about everything EXCEPT for being portable enough to fit in a pocket or hold upright like a book for extended periods of time.
I love my prime with the dock and will keep it(I think), but the nexus 7 is so thin and light that you can bring it anywhere and not even notice youre carrying it.
I am exactly where you are. I gave up on the prime as a daily user for entertainment because of its shear size. Its funny because I got that as a more portable device than my laptop. Now I have the N7 as a more portable version than my prime.
To the OP:
Here's what I would tell you, if you are looking for something that you will use just for web browsing, entertainment, networking, and a little productivity here and there; go with the Nexus. If you are looking g for something that you can write papers or reports, take notes, manage files on the go, and other productivity uses, AND then want to use for fun and games; go with the Prime, but go with the keyboard dock too.
What it really boils down to with me is support and development. Though both are made by Asus, they really, for lack of a better term, $h!t the bed with the prime. It began with updates every week to fix WiFi fallout and GPS issues,Then came I/o issues, then came others. For every fix they put out it felt like they broke something else. Now we've been promised jellybean and its been a month with not so much as a definite answer if we are getting it or not. Also the devs pretty much packed up and took their work else where, so there was no help in that aspect either.
The nexus however being...well a nexus will be backed more by Google and will get the treatment it needs. There is a plethora of development and you have the bonus of getting new OS as soon as it is released. Maybe its just me but I like to know those things are supporting me.
Hope my rambling helped.
Sent from my Nexus 7 using Tapatalk 2