Best solution to boost/extend network signal

The "best" and most reliable way is with wireless access point(s). However, some people don't find that solution acceptable because of the ethernet cable between router and access point(s).

Another way, which you didn't mention, is powerline adapters, which plug into an electrical outlet near the router and the wireless access point, using the electrical system instead of running an ethernet cable. Some powerline adapters include a wireless access point.