tab 7.7
Better and bigger screen (better for watching movies)
better audio(same as above)
better build
rear camera
memory card slot
can use for calling

nexus 7
better processor (gaming)
better software support
pure vanilla android experience

tab 7.7 (original set) is slightly more expensive than nexus 7 32gb 3G. If you don't mind,
price difference
software update
little difference to gaming or minimal lag in swiping the homescreen

Then tab 7.7