And while rare, sometimes a later revision is not as good. Revisions can be done for a lot of reasons:
1) To reduce costs
2) Improve longevity
3) Improve reliability
4) Similify manufacturing
5) Design change due to an internal part unavailability
6) Reduce weight
7) Improve failure detection and diagnostics
8) Add a feature
Generally, a later version is better than an earlier version. If given the option (which is exceptionally rare), I'd pick the later version.