The thing with USB wifi adapters is that if you're plugging them into the PC directly, the signal could be disrupted by the metal in your case, and if this is an HTPC, the metal in the surrounding equipment. You may be able to improve your reception by using a dongle cable to place your usb wifi receiver in a more prominent position to reduce signal interference.
I personally prefer to use DLink stuff...but you may be surprised to hear this but SMC actually makes decent "cheap" WiFi stuff that works well for the relatievly low price. If this is for a regular PC you may want to look into getting an internal wifi card that slides into a PCI slot...they're usually not as flaky as the USB stick adapters.
-= SsZERO =-