It has nothing to do with the torrent client...it's how well seeded the torrent is.
Think of it as....torrents are the complete opposite of 'direct' downloads. The more people that download a single direct download at a time, make it go slower.
In the world of torrents...the more the better. If you're trying to download an extremely un-popular file, it will be slow as hell. Direct downloads are hosted on a server, so when many users try to access it at once, it goes slower. Torrents are hosted on the PC of each person who's sharing that file...which is why more people make it go faster (and why it's easier to get caught with torrents...)