The best value IMO is something like the Asus 27", 2560x1440 (60Hz, IPS) for roughly $500.
http://pcpartpicker.com/part/asus-monitor-pb278q
If I had a 30" screen I'd just move it further away; I also prefer 16x9 ratio as that's pretty much standard now for content. In games, at 2560x1600 you'd be losing WIDTH unless you force 2560x1440 with black bars on the top/bottom which is not desirable.
G-Sync:
I really like how G-Sync works however it's going to be a bit expensive to start at $800 apparently for the Asus model once released (2560x1440, 120Hz, non-IPS). The non-IPS screen is good for two reasons:
a) less ghosting
b) higher refresh rate:
IPS:
IPS has better colour and wider viewing angles, but more ghosting and lower refresh...