I am sure Robin will want patches and not the changed files or ZIP
archives.
Indeed. It really is the best way for me to be able to review what has changed and to figure out what should be double-checked before committing. Also, if you happen to take your snapshot before some other changes are made to the code and then submit the whole changed file(s) then those other changes will be lost. Using a patch makes it possible to merge your changes with others.
I'm not sure. I haven't actually done PRs with these repositories yet, and since they are forks of a mirror of the main SVN repository, and since all change sets have to go up to the svn repo and then back down via the mirror and then back up to my fork, it's a little more complicated than the typical git repo... But I suspect that it will work okay and that overall the process on my end will be a bit more automated and streamlined.
In the end though it really just depends on what the contributor is most comfortable with using to make and submit the changes and either way is okay with me. If somebody is already familiar with how github and PRs work then I expect that submitting contributions that way will be a little more streamlined for them too.