I use m0n0wall on a Soekris net5501 box, installed onto a CompactFlash card. It's completely silent, and only consumes a few watts. m0n0wall is quite nice, and the Soekris box has 4 ethernet ports, which let me do unnecessary but fun things, like having two wireless networks (one encrypted, one unencrypted for guests, each of which has different access capabilities in terms of seeing my inside network/printer/file server). I've also setup VPN access to my home through m0n0wall. It has good port forwarding capabilities. m0n0wall has been rock solid with zero issues. The net5501 hardware is pretty minimal by today's standards, but is way more than powerful enough to run as a router.
I have two Linksys wireless routers running DD-WRT, but I'm using minimal features on those. That said, DD-WRT has been rock solid and has never needed a reboot.
(Incidentally, I use FreeNAS 7 for a file server running on a SuperMicro Atom server board and really like it, too.)
Home: Corsair 760T, Seasonic 760 Platinum, Z170 Deluxe, 6700k @ 4.5 GHz, NH-D15, 16G DDR4 2400, 850 EVO 1T, 840 EVO 256G, GTX 780ti, U3011, Linux, Windows 10
Work: Arc Midi, 650TX, P8Z77-V LK, 3770, 32G, 830 128G, 2x1TB, NVS 295, 2xU3014, Linux