OSS projects/tools are moving targets, and no software is bugfree or fulfills every need. Choosing a tool for daily work requires the investment of time and effort to learn the tool and fit it into one's workflow. Such an investment should be future-proof, which calls into consideration the maintenance status of a tool.
Does the project seem alive? Note that e.g. sheer volume of mails on a list may not be a good enough indicator, since a mature project may only see discussion on the occasion of a found bug, or the like. A much better indicator might be the responsiveness to such issues: how quickly are list posts followed up on? How old are the bug reports? How responsive is the maintainer/author/core team when prompted directly?
How long are the release cycles and are they time- or feature-based? Does the project release snapshots? Does it maintain separate releases for stable and unstable/in progress code? Is the code repository public and is an effort made to make sure the code checked in compiles and runs?
Does the project use a publicly available (and usable) bug tracker?