In Go's wiki page on Github, it is told to be set in ~/.bash_profile:
https://github.com/golang/go/wiki/Setting-GOPATH
In this StackOverflow question most of the top voted answers suggested to be set in the ~/.bashrc file:
how do I SET the GOPATH environment variable on Ubuntu? What file must I edit?
I have read that ~/.profile is perhaps the best way to set environment variables. Is there a reason that ~/.profile is not used to set $GOPATH or is it just a matter of preference?
If you have a .bash_profile file already, you can use it, else use .profile. You could also source .profile from .bash_profile and add anything you need to .profile instead; see this answer for more info.
.bashrc?If you add environment variables to .bashrc, you can experience things like duplicate PATH entries, but it also means those vars are only available in a process launched from a shell. For GOPATH, that usually isn't a problem, but it is PATH-like, so you should stick with the shell profile to avoid any potential issues.