I use Pirate Bay and BTJunkie, there are others.
Speeds vary like Windows from slow to 1,000 KBps depending on your connection, peers, seeds.
Torrents are real easy to set up in Ubuntu.
Click on Applications>Add/Remove, let it load up.
In 'Show:' box at top select 'All available applications'
Then on left side where it has 'ALL' highlighted, drop down and highlight 'Internet'.
After they load, scroll down the listed apps and select any of these bit torrent clients for installation:
Transmission,
Deluge,
Vuze/Azureus
You simply put a checkmark in the box in front of the app, then hit the 'Apply changes' box at lower right and Ubuntu will auto DL and install the apps you select, then tell you when they are installed and ready for use.
I lke using 'Add/Remove' for adding apps.
You can also use 'Synaptic Package Manager' if you know exactly what app you want to install/uninstall.
i.e., say you want to install 'Vuze'
Click System>Administration>Synaptic Package Manager:
Put in your password when prompted, then let it load.
Once loaded type, Vuze, in the search box at the top, when it comes up, checkmark it for installation, once it's confirmed, click on 'apply' and Ubuntu will do the rest and tell you when it's done and ready for use.