The classic router for this purpose was the Linksys WRT54G, but that is getting very long in the tooth and does not support 802.11n or 802.11ac.
The current reasonably priced (about $100) pick that supports everything and is a *working* 2.4ghz and 5ghz 802.11ac router with OpenWRT or DD-WRT is:
TP-Link Archer C7 V2 AC1750
Manufacturer Info is here -> http://www.tp-link.com/en/prod...
It can be re-flashed with either OpenWRT or DD-WRT to provide firewall and a variety of VPN types. It also has enough flash to add other features and given that it includes 2 USB 2.0 ports can also used as a low power (compared to a full hardware PC) internet server.
The disadvantage on this router is that it only supports 1750AC and not 1900AC and that the USB ports are only 2.0. There are routers that cost a lot more that provide both 1900AC and USB 3.0, but they also do not currently FULLY support OpenWRT and DD-WRT.
My personal experience is that OpenWRT is more module than DD-WRT. This makes is easier to pick and choose "packages" in any configuration you'd like. For instance, I added the stunnel package to protect a IP video camera that did not provide HTTPS for remote home monitoring. Now the router provides necessary HTTPS for that use case.
If you are looking to use either DD-WRT or OpenWRT check their home pages BEFORE purchasing a router so you know that it is fully supported by each.
The router to AVOID at the moment appears to be the Linksys 1900AC which the manufacturer FALSELY claimed in their sales literature at launch supported. It still does not.
You can view info on the OpenWRT project here -> https://openwrt.org/
And the DD-WRT project here -> http://www.dd-wrt.com/site/ind...