The best route, by far, is to run Ethernet cable to all devices. Hardwire is far superior to anything.
Next up would be: Adding an access point, going Powerline or a more powerful N-Router.
If you can't go wired, I'd put the Wireless Router in the center of the house on the second floor and put a wireless access point on the main floor which should improve reception in the basement
Getting an access point means you still have just one wireless network.