What is the best way to merge my files from 2 different Macbooks?

What is the best way to merge my files from 2 different Macbooks?

I have an old Macbook Air that has files on it (mostly images but probably some docs too) and I'd like to add them to my newest Macbook Pro.

I've been using a Macbook Pro for a few years now and it has a lot of newer content on it that is not on my old Mackbook Air, so I'd don't want to overwrite my Pro with a backup of the Air content. I just want to add any content from my Air that isn't on my Pro.

Any idea how to do add the missing content to my Pro without just adding everything and ending up with a bunch of duplicates?

Thanks!

~Andrew