There's a lot of negative comments on the ac AEBS/Time Capsule here, but I have to say my ac Time Capsule is giving me *excellent* service on all my ac/n/g (and even a b) equipment.
The Asus 66 is certainly faster and has more user-configurable features, but (i) its not faster by leaps and bounds (the AEBS/TC is nearly as fast), and (ii) the "limited" feature set on the AEBS/TC is not that "limited," and in any event is only a concern if you are one that uses a lot of advanced features.
To each their own, but I went with the ac TC because it in the real world the performance difference is hardly noticeable, and it keeps my MBP and router in the same "ecosystem" of Apple -- i.e, known-compatible software, easy set-up/use of Time Machine, and no opportunity for two separate companies to point at the other as the source of any problem that crops up.
My primary point is there's more to router choice than performance specs -- be sure to consider your entire use situation before choosing!