Transmission ( http://www.transmissionbt.com/ ) is an open source torrent client with a nice web interface (as well as native interface) just like Deluge.
I think it is somewhat lighter resource-wise (I'm running it on my NAS), but apart from that I don't know the exact differences between Deluge and Transmission, but I thought I'd mention it for completeness' sake.
I suppose I did not place the same emphasis on "great" as you did. Alternatively, I couldn't name a "great" Windows UI offhand, anyway.
However, my experience is that some Qt apps on Windows behave normally, and depending on the application (but in this case, especially just the need to manage torrents) a web UI works just fine and avoids the waste of developer hours fighting against the local platform's quirks.
For my enlightenment, what do you consider as an example of a great Windows UI?
I think it is somewhat lighter resource-wise (I'm running it on my NAS), but apart from that I don't know the exact differences between Deluge and Transmission, but I thought I'd mention it for completeness' sake.