welcome to 2016
S3 is widely spread, usage is easy and cheap, other clients support S3 - hmm, some well (Cyberduck, which I don't like for the UI), some less (Transmit, Forklift - no v4 support).
What about Yummy? Amazon S3 (both v2 and v4) and Glacier would be a big plus!
It's that essential in my opinon, that I even signed up for this forum and reactivated that old thread