I gave away my C720 4GB and C720 2GB models but not because I didn't love them. The former to a colleague and the latter as a gift. I miss me some Chromebook!
After being without my Chromebooks for quite awhile (I was primarily using my Mac-book Pro) I decided to see if there were any new Chromebooks out there and if so, if there was a compelling reason to pick something up other than a C720. I'll cut straight to the chase...there is no compelling reason to purchase anything except the Acer C720.
The fact is, unless you really feel like spending more money or need a bigger display, this Chromebook is about as big a bang as you can get for your Chromebook money. You might want to go with the 4GB model if you typically roll with lot's of tabs open, but in practice I have not had issues with performance.
I've researched a bunch of different models (HP, Samsung, Asus), read the reviews read the specs and checked them all out at Best Buy (don't ever ask their sales people questions if you want to get the correct answers).
According to the Acer specs, you'll enjoy 13 hours of battery life for their HD (1366x768) and 11 hours for the Full HD model (1920x1080). I'd probably cut that down by 10-20% depending on how bright you like your display. It also adds about 1/2 pound to the weight over the original C720 (2.76lbs vs 3.3lbs).
I love me some Chromebook!