Due to its nature NodeJS is performance-wise still a better solution than any Python-based one, at least for now. And it's async in core and by rule, thus nodejs modules are async too, yet no async-motto is coupled with Python, so it's much harder to get async-ready libs suiting Tornado. Therefore COTS-wise NodeJS is actually also a better solution.

But in the end the most important thing is whether you're more familiar with Python or JavaScript and which solution will be more productive for you. Unless you're going for really large scale project and want to shorten your time by using existing modules, Tornado is obviously as good as NodeJS.

Loosely relevant: http://amix.dk/blog/post/19484#Comet-with-node-js-and-V8