Google Drive, because I got a "free" 100gb plan for 2 years thanks to my chrome book.
I use this app for auto upload:
https://play.google.com/store/apps/details?id=com.nekjo.photouploader
Works for me.
Skydrive since i have 25 GB of free storage!!!
Skydrive was dog slow for uploads when I tried using it last year. Have they improved that?