Embedders of V8 should generally use the head of the branch corresponding to the minor version of V8 that ships in Chrome.
To find out what version this is,
- Go to https://omahaproxy.appspot.com/
- Find the latest stable Chrome version in the table
- Enter it into the "Translate a Chrome verison to a V8 version" box below the table.
- Ignore the last two parts.