I personally prefer [Semver][]. I think it's reasonable, simple, and makes sense. But as a good Haskell citizen, I'd like to be [PVP][]-compliant as well. Here is a bit of a graphic showing how the two systems are almost the same:
PVP: A . B . C . ...
Semver: Major . Minor . Patch
^ ^ ^
| | |
| | ` increment for other changes
| |
| ` increment on non-breaking change