Stay away from the WRT1900AC nothing but problems for me. Go with the RT-AC68P from best buy.
I have to say that the latest firmware for the WRT1900AC is not bad. I'm not using 2.4GHz. band, just 5GHz. wireless, but it looks pretty good from that point of view. On the other hand, the web admin GUI is very limited, the features are pretty limited, and there is no reliable open source firmware for it since Linksys/Belkin seems reluctant (or unable) to release a decent version of the wireless driver source for open source use.
So, for me, it wouldn't be my first choice, especially given the higher price. But if you're looking just for a routing/wireless appliance, don't need (or want) much monitoring capability in the admin web GUI, or expect features like a VPN or extensibility, then it isn't a bad choice.