I use a single Asus RT-AC66U at my condo. It's running stock firmware and is perfectly stable and feature-filled.

I don't have any 802.11ac clients to test with, but the 802.11b/g/n range has been fantastic. I'm on the 3rd floor of a brick and stucco building. I can easily get a usable signal in my garage on the ground floor. I can drive maybe 100 ft away before losing signal on my phone.