All versions currently available are essentially "testing" versions. Daily snapshots of the work in progress, or the bleeding edge. Statistically speaking, any one build is probably equally likely to be unstable. That being said, "current build" is less likely to have the more glaring bugs, simply because if a change introduces a major problem, usually it gets fixed within a few hours, if not less. If that major problem lands on a daily, well then, that daily will always have it, while the current build goes on changing with each update.
Until there's a "release", there's really no officially sanctioned "this one is more stable than the others" version, since we tend to look at what we need to fix or improve now, rather than what it was like yesterday or last week.