Best branch to track for creating a pull request in GitHub

Good afternoon,

I have a set of bug fixes for Liquibase that enable it to function for DB2 on z/OS that I have been maintaining in my employer’s SCM repository; this was tracking the 3.9.x release branch about a year ago before I had to move onto other things.

I picked up the project I was working on again that uses Liquibase and DB2 on z/OS, and now that my employer allows git over https access to GitHub through their proxy server, I was hoping to create a pull request with my bug fixes with the hopes that I could get the changes into a future version of Liquibase.

My question is - which branch in the GitHub repository would give me the least amount of trouble with regards to volatility and highest likeliness to get incorporated into a future version of the codebase?