A hard wired connection is obviously going to be best. These days I would say the USB adapters work as well or better than the PCI cards. It really depends on the signal output. Generally, the bigger the antenna, the better the signal strength.
As far as reliability, I couldn't really say. I've had several of both type of wireless adapters. Some work really well and last a long time. Others dropped the signal frequently, and died early.
The recommendation I usually make with any wireless adapter, is that you only install the drivers and not the included software. The Windows wireless config utilities almost always work best. When that's not the case, it's usually because the drivers for that specific adapter suck or need to be updated.
