You can actually compare files natively right in Sublime Text.
Navigate to the folder containing them through Open Folder… or
in a project
Select the two files (ie, by holding Ctrl on
Windows or ⌘ on macOS) you want to compare in the sidebar
Right click and select the Diff files… option.
Compare Side-By-Side looks like the most convenient to me though it’s not the most popular:
UPD: I need to add that this plugin can freeze ST while comparing big files. It is certainly not the best decision if you are going to compare large texts.