I only use SkyDrive. I use Windows 8.1 on my PC and it's the de facto choice for cloud storage. It also doesn't hurt that I have a grandfathered 25GB plan since I've had the account forever.
It has Camera upload on iOS. The UI doesn't suck like Box's app, and the Account on a whole is used by me so I don't have to create yet another account for it like I would have to with Dropbox.
For people who have a Google Account then I can see how Drive could be in a similar position, especially if they use a Mac instead of a Windows 8.1 PC, but I've had a lot of trouble justifying creating yet another account and keeping it open for something like Cloud Storage when the PIM services I use come with a completely capable solution that I can use with the same log-in.
I certainly cannot see myself using a "combo" of 4 services, since they are so bad when it comes to shuttling data between them without resorting to yet another third party service/account to facilitate that... Lol My way these days is to keep as few accounts as possible, so the day before I got my iPhone I moved everything over to iCloud or Hotmail and deleted the Google account less than an hour after I got back, after making sure I had moved everything over
I would go crazy trying to juggle so many accounts.