Ask HN: Most stable MySQL version?

I need to complete some unfinished work for a company which doesn't have a regular dba and it appears their developers are working with different versions of MySQL from 5.0.33 to 5.1.28.

I've been working with PostgreSQL for a long time but haven't done much with MySQL before and know relatively little about the overall stability of different MySQL releases.

Counting the open bugs for each version at http://bugs.mysql.com leads me to believe 5.0.33 is the most stable but I'm curious about what people with a more solid background in MySQL think is the most stable?