Dropbox, Yandex.Disk and Google Drive. I use each one a little, somewhere I like the very convenience and intuitiveness of the interface, as in Dropbox, and somewhere I am attracted by a large volume and ways to increase it for free (+ 32 GB for enabling cloud sync on a smartphone), like Yandex.Disk. Another plus is purely regional, since Yandex is mostly a Russian service (even despite the fact that its parent company is in the Netherlands) - it also has servers in Russia, including the regions, so the download speed is always maximum.
I liked the Google ecosystem, and I stayed in it. 15 free gigs of course are not many, but unlimited photo storage. And these are symbols that are always missing.
I am using Yandex Disk. For some reason, I generally prefer Yandex services, but when I heard that for the connected autoload photos they give + 32GB forever, I definitely think that we should use it.