[stomachmonkey]

What you want is known as a dual band router, operates in 2.4 and 5 ghz specteums.

I know you are looking for the easy answer but the thing about wifi is it operates at the speed of the slowest connected device.

Obviously without knowing much about your current devices hard to say what speed a, b, g or n they run on but seeing as they are not really communication devices, pass large amounts of data, its safe to assume they are slow.

Get the dual band and put all the slow / unknowns on 2.4 and all your newer know N a/c devices on the 5 spectrum.

Now there is also no gaurantee a newer router will provide broader coverage so if you can run some cat 5 close to your dead zones you may just want to run two wifi networks.

Saves you from having to reattach those other devices to boot.