Works Deluge delivers the goods. Encryption, DHT, uPNP etc. Pretty much everything you need in the face of mean ISPs, throttling, and leeches.
Actively developed Deluge is rapidly improving with quality and features. The development community is responsive, if a bit hostile at times. The cons below have a chance at being eliminated in the future, if this continues.
Non-judgemental Deluge doesn't try its hardest to stop me from seeding, it doesn't try to trick users etc. The system to stop seeding is extremely simple and I hope in the future it's extended to shut the whole thing down when there's no active torrents left.
No good plan for end user distribution Traditionally, Debian users wait for upstream releases to enter unstable, and Ubuntu users sometimes wait for the next release. The Debian model works great when a DD is involved, and the Ubuntu system works okay with -backports and PPAs. Deluge has managed to avoid both of these, but also avoided providing the usual sources.list repo. They've been grappling with how to better serve their users in light of the cost of being popular and rapidly changing. Ubuntu represents 50 percent of the bandwidth and 80 percent of the downloads -- if anyone (Jono maybe) reads this, perhaps it's nearly time to form an outreach.
No significant memory savings Azureus has a reputation for being fat, and I was hoping that Deluge would be lighter. It was at first, but with new versions came new features and new weight. My primary reason for switching was to reduce memory usage. DHT alone seems to cost 5 resident memory MB and 3 writable. I'm not sure how to best analyze memory usage. Comments welcome ;)
For me now, Deluge is the app to beat.