I'd be tempted to suggest something with an external aerial, such as this or at the very least, for the OP to consider using a USB extension lead, or plugging the adaptor into a USB hub.
Only mention it because sod's law suggests the PC will be a large metal lump in between the USB adaptor and wherever the router is. (Even if it doesn't block the signal completely, it could have a significant effect, which is why some of the wi-fi cards have 3 aerials sticking out the back.)
I know most laptops with an adaptor built in represent a chunk of 'body' surrounding the internal wi-fi card, and perhaps some designs work better than others.
When one of my clients gave up on wi-fi, replacing with data-over-mains adaptors for reliability reasons, I was given their old Belkin adaptors (oh, and guess what, the later version had two aerials not one). This particular Belkin adaptor has a length of cable before the USB plug, which allows the user to position the unit for the best signal possible.
I found that moving it perhaps an inch can make all the difference between connecting to a distant router (*) or not.
You can still get units (working at higher speeds than that old Belkin unit) with an extension cable - see this one at Play.com - 17.99 including VAT with free delivery.
(*) 75 to 90 feet, connecting to an insecure router at the home of someone in a different street (but line of sight from the bedroom window!) - I know which house, just not where the router is within it !!!