I argue that twisted is better for most practical uses of comet.

Tornado mastered only the "have lots of suspended connections" thing. Many of the examples involve blocking for processing one of those connections. What's the point of having 20k connections terminated on an http comet connection if you completely block the entire event loop to service a single one while you make another network connection (e.g. memcached, mysql, etc...).

In this regard, most real life comet apps are doing more than http. To be fair, tornado did ship with a yet another python http client, so you can at least use it with a database that speaks http without blocking, though without chainable deferreds, it's hard to do the exact right continuations required to chain these events together without locking the event loop.