Low quality connection: is it my internet provider or my router?

"Check with a wired connection directly into your modem - if it persists, it's your ISP. Then check with a wired connection going through your router - if it persists, then it's a problem with your router. Finally, if that all works fine, it's the wireless portion of your connection that is bad. Check with another computer to see if it's your wireless NIC or the router.

Be sure there are no electrical obstacles between your computer and the router, you'd be surprised what can interfere with wireless connections."

The first thing I'd do is check that you're not using a default, out-of-the-box SSID on your wireless router. If this is the case, and a neighbor has the same SSID within range of your PC, then it's very possible (probable) that your PC is bouncing back and forth between your network and your neighbor's and you're experiencing poor performance due to the low signal that you have from your neighbor's router.