Well Facebook sharing is cool but limited in resolution. What if you want to share the high resolution images?
Amazon Prime now offers unlimited high resolution storage for five family members. It’s sort of free if ur amazon anyway
Two sort of good choices: Apple iCloud (for low resolution only but essentially unlimited) and Yahoo’s Flickr (for as long as it lasts up to 1TB)
iCloud photo sharing is free and unlimited but only limited resolution.
Apple doesn’t advertise it but you can store original high resolution photos up there with some sort of bizarre limits. The biggest limit being 100 users who can contribute per album and only 100 albums per login and the images are down rezed to 4Mp.
Neither of these are too severe because you can and probably should probably create a dedicate login for sharing from say a group (e.g. email@example.com, firstname.lastname@example.org,…) if you have more than 100 albums (that’s a lot by the way).
For non Apple users, you can use web link sharing which allows people to see the photos if they pass a link around. That’s a bit of a security risk, but let’s presume for now that this is for public sharing and small group interchange.
Flickr gives you 1TB free
The second recommendation is Flickr. It has a 1TB Limit per user ID and stores full resolution. It is owned by yahoo however so not clear how long that lasts.
The biggest problem with Flickr is that they really want you to have a Yahoo login to use and comment on the site, although you can of course pass the links around.