As far as I know, gnu is generally more focused on park, and libs are generally a bit stiffer and more all mountain oriented. Both are made by Mervin, so they'll have similar tech. That said, I saw a ton of gnus in the xgames.
I'm going from a burton supermodel 159 to a lib tech trs 154. I rode the riders choice in a 153*?* and was just a touch chattery at high speeds, but the trs is a bit stiffer and has a better camber profile for my taste.
Mervins hybrid profiles seem to be well respected as quiver killer decks. I think they has a very unique feel that is easily adaptable to most conditions. Some are just more geared towards park, and allmtn/pow. Idk if id feel conpletely comfortable having it as my only deck as I've always ridin straight camber and that's what I prefer. But well see when it gets here in a week. Do some research , demo a few if you can and you'll know if you like it pretty quick.