I only really know one of these services - but what I really like about Google Photos is how seamless it works.
On the phone, I take images and they are backed up whenever the connection allows for it. I can then free up space on the device, but still view individual photos whenever necessary. They are also available to me via the web interface anywhere.
On the desktop, I basically have two folders for images I download from my DSLR - an "incoming" folder of unsorted images, and a "backup" folder where I arrange photos any way I deem necessary. That second folder gets uploaded to Google Photos as well, via their "Backup & Sync" app.