My $ .02
In my opinion, the GR-2 34L provides a little more organization via the front compartment; I like to use this section to stash my jacket along with the bag I use to hold my in-flight essentials. There are also four built-in pockets of varying sizes for other "small stuff". The main compartment will hold my clothing. I normally do not travel with a laptop, so I use that space to hold a small (15") Eagle Creek folder to hold my collared shirts.
That being said, I still use the GR-1 more frequently, especially for international trips. There never seems to be a worry about compliance with carry-on requirements/dimensions. It's profile is slimmer and just works well for my personal needs. Also consider that the GR-1 is about $ 100.00 less.
All things being equal, I don't feel the additional 8L of payload is that advantageous. Go with the GR-1. There's a reason it's the company best seller. It's not just for rucking.