All hardware can break down, and wireless networks don't like solid block walls - it's a matter of compromising.
I tend to use Belkin N1 routers
click here in my office because they are reliable and give good coverage. At home I'm currently using a BT Home hub, and I'm pleasantly surprised - it runs well, and the coverage is fine.
If reliability and speed over a wide area is an absolute necessity you should really be considering a wired network.