When properly set up all bittorrent clients run at about the same speed.
This has some info on the better clients and links to speed optimizing guides for them:
Gizmo’s Freeware: Best Free BitTorrent Client
http://www.techsupportalert.com/best-free-bittorrent-client.htm
I use bitcomet
i also have 1mbps and it works well with me
just make sure of the health of the torrents u use
and make sure of the numbers of the downloaders and the uploaders
seeds and peers
the uploaders have always to be high numbers
Good luck