Don't use either. I tried and failed with both. Expensive hardware and a PhD required to go through all the config options. When I did get both to work, they were very slow and I kept getting replication issues and bricks that wouldn't heal.

This cost two months of my life and I was not flavur of the month with my employer.

I eventually tried lsyncd ( https://axkibe.github.io/lsyncd/) and it works like a charm. It took me about a week to get a decent setup going, but it has never let me down since, can handle large numbers of small files (similar to yours) and smaller numbers of large files. I use unison ( https://www.howtoforge.com/tutorial/unison-file-sync-between...) for web server pairs.