What is the fastest, smallest, easiest way to use bitTorrent on an iPad 2?
If you have a Mac, the simplest solution might be to install Transmission on your Mac, use its web interface (which looks great on iOS), and let the torrents download on your Mac.

From iOS, you can control almost everything, and add torrents by pasting in URLs, since Mobile Safari doesn't let you do file uploads. It's not exactly what you asked for, but if you don't absolutely need the download to be happening on your iPad, this is much simpler.

If you really need the files to end up on your iPad though, you could try something like this.