When comparing Sublimerge vs Diffy, the Slant community recommends Sublimerge for most people. In the question“What are the best diff plugins for Sublime Text?” Sublimerge is ranked 1st while Diffy is ranked 5th.
Ranked in these QuestionsQuestion Ranking
Pro Three-way diff allows easy merging of files
Pro Highlights intraline changes
Pro Built-in support for Git, Subversion and Mercurial commands
Sublimerge automatically integrates with your version control history, and lets you compare between revisions, branches, remotes, and the staging area.
Pro Can compare to clipboard contents
Pro Provides inline side by side diffs
Diffy computes a diff between two panels using sublime texts multi panel feature, and highlights the diffs inline.
Con It's NOT Open Source
You can't fix or, implement nothing. And when the developer abandons the project you will be left in the lurch.
Con It's not free
Nither as free price nor as free in freedom.
Con Cannot compare text within the same file
Sublimerge can only compare entire file diffs, but not two selections within a file. Comparing within files can be useful for example, by refactoring two similar functions to use a shared function. With Sublimerge, you need to copy the sections into two new temporary tabs and compare between the two. This can be cumbersome, as if you have another untitled file, you won't be able to know which one is which.
Con No version control integration
Con Diffs cannot be cleared if you leave 2 panel mode
If you create a diff in 2 panel mode, then switch to 1 panel mode, the clear diff binding does not work.
Con Diffs don't live update
Diffs are only computed when you call it via key bindings, so if you edit the file after generating a diff, the old diff will still be there until you clear it or regenerate it, which can be kinda confusing.
Con No command pallet entry
The only way to compute a diff is through key bindings, and the default key bindings are
ctrl+k, ctrl+d for diff, and
ctrl+k, ctrl+c for clear diff, which will require some memorization or customization.