The simultaneous dual band N routers (N600) aren't but maybe $20.00 more than the single band models. I don't see a good reason to stick with a single band. However I agree fully with RealBeast. 802.11ac isn't fully standardized yet, and easily triple the rice of N600 hardware. Don't bother.
I like my Linksys EA2700, it's not perfect, but from a price / performance standpoint, I am quite pleased. Signal is more than sufficient for my 2000 sq/ft space and then some. (I get WiFi in the yard as well...)
You can get the N750 and N900 routers, but unless you have a device that needs it, or you need the greater signal / radio strength, they are a lot more expensive for additions you probably won't be able to take advantage of...