Question about wireless adapters

Alright, so i have done some research about the pros and cons of an internal and a usb wireless adapter. I have a wireless network setup in my house and my computer is the farthest from the router. I am currently using a usb adapter and it works, but I only have half the possible signal. My girlfriend recently got a laptop that came with an internal adapter ,as they normally do, and when I connected it to the network while being in the same room as my computer it had 4 out of the 5 bars. It had a much better signal then my computer which uses the usb adapter, now I have read that usb are better and pick up signals better, but what could be the problem. Could it be my usb adapter, should I try another or try an internal? Thanks in advance for the answers

Alright so just to make sure I understand lol since im slow, you think I should drop the usb and get a pci for the desktop instead? Thats what I was thinking but I wanted a second opinion lol.

Exactly -- before spending money try also changing channels, relocating cordless phone base or video sender away from computer or router, try raising the router above furniture level.