Chrome: Although Chromebooks have limited storage space, they make a great BitTorrent machine since you're less likely to be affected by malware. JSTorrent is a BitTorrent client that works on any Chromebook.
The interface makes it simple to add torrents. Just right-click on the link and it adds it to the downloader. It run well even on the low-end ARM-based Chromebooks. I tried it on my Acer C720 and it worked like a charm. A few other free clients exist for Chrome, but JStorrent is easy to use and has excellent support.
As you'd expect with any torrent software, you can pause and prioritise your downloads as needed. It isn't quite as feature-filled as some desktop clients, but for Chromebooks, it works well enough.