There's probably an easier way, but this seems to work assuming you have Google Drive or something similar. I did this on a Windows PC but I'm guessing it'd work on a Mac.
On your phone, create a new album. I called mine "Faves"
On the phone, add all your Favorites to the "Faves" album. For some reason at least on my phone, Favorites don't show up as an upload choice in Google Drive, but albums you manually create do.
Open Google Drive on your phone.
Create a new folder on your Google drive (I used iPhone Faves).
Navigate to the new Google Drive folder, then upload all the photos in iPhone Faves to Google Drive
Open Google Drive on your PC or Mac
Download all the photos in the iPhone Faves folder to the local drive
Once I'm sure everything's good, I delete them from the Google Drive folder and the iPhone Faves folder.