I'm an s3 user and like the phone. Having just went through this with my father, I would seriously consider not getting him a smartphone unless you know for sure he can use it.
You know your father better than anyone else but a few things to consider:
1. Vision - will he be able to read all the content on the screen? Zoom doesn't work everywhere.
2. Reliable - dumb phones are reliable and don't depend on computer software for anything. No matter what your opinion is smartphones are not as reliable as dumb phones. If you need a reliable phone for your dad that isn't prone to 'vulnerabilities' outages or being dropped.
If you want to get your father the features of smartphones, get him a separate tablet, 7in or 10 in depending on his vision. Your dad will be annoyed at having to scroll all over the place on a phone. You can even get him a tablet with a built in cellular modem.
That way when the tablet locks up or he drops it, he can call and blame you