I'll start by voting and telling my reasons, you do the same:
1. A somewhat nice GUI.
2. Good number of features by default.
3. Has a good plugins system.
1. The GUI responds slower because it is written in Python.
2. Can get clunky and feel bloated at many times.
3. The handling of the BT protocol isn't developed by the Deluge team, they are using libbittorrent which is written by others thus making them dependent on them.
4. The pre-compiled package is very large compared to other clients.
1-Written entirely in C++ which makes it lightning fast.(both the GUI and the core)
2-Has less resource consumption.
3-The pre-compiled package is about 330 KB only !
1-Has a very strange GUI.
2-Has very few features by default.
3-The torrent info provided isn't enough and the progress bar isn't readily understood.
4-No plugins or modular system.
The winner in my opinion: Deluge
The GUI and the plugins win me.
I guess I can live with the slow GUI
What do you say?