Torium is a good candidate - its based on libtorrent, has simple GUI and torrent properties are in a new window, so not taking up space. I tried porting it, but its based on Gtkmm and the Maemo 4 Gtkmm has quite a number of features removed for simplification, but they use them (mainly setters and getters), so it required quite a bit of work to get it in shape.

If Maemo 5 has Boost (or in repo) and Gtkmm is not simplified, then it would be a good candidate because of its simple GUI and good speed (which all libtorrent clients share, the others are Deluge and Flush, but they're bigger).

http://bithack.se/projects/torium/screenshots