Nobody has mentioned this so I'll throw my two cents in.
First, it would normally not matter whether you used the most powerful desktop in the world or an average laptop. What your internet provider allows you to have is what you have.
Having said that, there could be one reason why one computer or another uses more bandwidth - a virus!
Yeap, the life of a virus is a hard one. Always using your bandwidth to do dastardly deeds.
I know my wife has a few hundred viruses when she starts to complain how slow her computer/internet is.
She thinks that the way people get viruses is by going to bad websites (porn). One time I removed over 300 pieces of malware/viruses from her computer. Love it.
Anyway, there are a couple of ways to keep track of unusual activity.
For your needs the best might be to monitor your bandwidth usage in real time.
A very simple, and low CPU usage, program is
Bandwidth Monitor by Rokario Software. There's a free version and a paid version. You'll want the free version.
The scale is relative. With little or no activity you'll just see a bunch of small bumps with an occasional spike or two. BUT check the numbers, those spikes are relative, remember. Start a download and you'll see the scale change.
Watch these two numbers for a better idea of the size of the upload/download sizes.
There are also programs that record the amount of bandwidth a computer uses, but you'd need to keep a running total of all computers on your internet connection.
If you feel tech savvy, you could find some free software such as
PRTG from Paessler. It's free and relatively easy to use, but will be far more complicated than "
Bandwidth Monitor". It is, however, capable of monitoring EVERYTHING passing through a
(home in your case) network.
It's amazing how much you can learn, IF you want to dig deep enough. You will work hard for that knowledge though.
One thing to remember when you see network activity, when you haven't initiated any, is that there are valid causes for that activity (such as programs checking for update) etc. in the background.