What I used to have was only My Photo Stream. It was turned on within my phone and on my Mac/Photos. I used to backup my photos every month, for years. Then suddenly, the "My Photos" folder refused to appear within Photos. I tried many different things, and finally was able to get it to appear, but it only displayed a few selected photos. I tried everything to get it to sync, to no avail.
So I went ahead and turned on iCloud Photo Library, and My Photo Stream. I selected the option to upload all photos to iCloud and store all originals on the Mac. My hope is that this will put everything in both places and I can then backup my library on my Mac. My library is 142GB, so I am still waiting for the sync to complete.
However, I can take new photos on the iPhone and they will appear in iCloud Online, but not in Photos on the Mac, so I still don't think a proper sync is taking place.