Modern off-the-shelf routers are generally equivalent in their WAN performance... just get one with a 1Gb/s WAN interface. If you are worried about how these routers will affect your wired mining performance... then don't. Your only deciding factor will be wireless performance, which you shouldn't be mining on a wireless connection anyway.
So, the short answer is pick the router that works best for your desired wireless performance. If you must have dd-wrt or tomato compatibility, those distros have some suggested hardware lists.
I run my own linux distro as a router/firewall on a virtual machine. I'm partial to IPFire. Then I have a decent wireless router downstream with the DHCP server turned off to provide wireless to the home. This effectively makes the wireless appliance a wireless switch.
What do you think of the Ubquiti Edgerouter X? $50-60. I heard it comes with a 100 page manual with tons of configuration options. WOndering if I could just use that for LAN/WAN and have my existing WIFI router turned into a switch like you have.