Ask HN: What scenarios is Python 3 a bad idea to use, versus Python 2?

For years, I've been avoiding Python 3 in production out of concern for poor library support, a lack of an installation base on end user systems (although most of my code runs on my or my employer's servers), and so other Python 2 developers could comfortably contribute to my code.

There have been a series of articles over the years about the Python 2 vs 3 issue, but now most of them don't reflect the state of affairs on today--August 21, 2014.

The website http://py3readiness.org/ puts us at support for 270 out of the 360 most important packages. I suppose that's enough for most projects, but what scenarios is Python 3 inappropriate for?

On the other hand, Paul Graham's "Beating the Averages" suggests the use of the best language possible for server software, but it's still not completely apparent to me whether Python 2 or 3 is the better language in that context.