uTorrent vs. Azureus... uTorrent slows network, Azureus doesn't?

[squint]

When I use uTorrent to download torrents, my brother, who works at home, complains of slow internet speeds. I experience it too on my own computer (the one I'm downloading torrents on with uTorrent).

When I use Azureus, this doesn't happen. Our internet is just as fast as it is if I'm not downloading torrents.

What could be the cause of this?

Is there an obvious troubleshooting step that I could take that I'm missing?

Thanks for your help in advance!