Granted, Amazon Cloud Drive has more storage, but I doubt they will be as easy to use as Dropbox. At least they have a lot of catching up to do before I consider them
They got a much larger community as compared to Dropbox. With the amount of offerings they have - this is going to be huge. They will have information of what music you like and what not. If you pictures uploaded - they might start a photo printing service soon. The advantage Amazon has in this - it's image as a reliable / trustworthy seller. I already got my Amazon MP3 update on Android and it's working.