Using Visual Studio Code (version 1.11.2), I can see a side-by-side graphical diff of my current changes very easily by clicking the Source Control button in the left p
You can use an extension for this.
Two good options:
Gitlens: https://marketplace.visualstudio.com/items?itemName=eamodio.gitlens
With this one, you can use the >GitLens: Open Changes with...
action to compare with any branch (local or remote).
You also can use Git History: https://marketplace.visualstudio.com/items?itemName=donjayamanne.githistory
You can see the entire file history and compare with the current version with the >Git: View File History
action.