I find "beyond compare" to be a very good merge tool. It's not free, but not very expensive either, and works well with git.

(I'm not affiliated with them in any way)

Beyond Compare is a good tool. It allows to compare full directories, ignore whitespace, etc.

I recommend Perforce's as a merge tool because it is better than average at the specific task of merging.

Perforce's P4Merge is the least-worst (free) merge app I've found for Mac. I use it for git and hg. That said, I'm always open for recommendations for something better.

btw, you can download P4Merge (aka "Helix Visual Merge Tool") here:

https://www.perforce.com/downloads/visual-merge-tool

https://semanticmerge.com seemed unique to me, and https://www.gmaster.io experiments with going farther.

Semantic patching can be good to resolve conflicts, but version control operates with non-semantic changes.

This can be frustrating at times, since many code bases cannot be reformatted or refactored because it affects version control history.

Yep, hated perforce, but the merger is quite good. In fact so good that for a time I used it standalone on git and svn projects too.

Nowdays I'm using webstorm and it's differ/merger is very very good, but ymmv.

IntelliJ (and specialized versions like Webstorm) has a very good diff tool, integration with version control, etc.

An underused feature is "local history", which is a local cache of all local changes. This can be a lifesaver sometimes.