I prefer Dropbox to Box, as many third party applications have built in support for Dropbox, and their Windows and OS X clients work perfectly.Box.com has the 50GB program too. Right now, it's only for Xperia and LG Android devices, as well as the (cough, cough...) iph.ph.ph. Oh damn... You know what I'm saying.
I have 50GB for my RAZR MAXX and got it back when the promotion was open to us. Oh, and it's for LIFE!! (not 2 years).
Wednesday, February 29th, 2012
Got Your Free #Box50GB? Now See 4 Quick Tips to Make the Most of It
By Mark Saldaña, Social Media Manager
This promotion has ended, but don’t fret! If you have an Xperia or LG Android device, you can take advantage of our 50 GB offer until December 31, 2012.
50GB | The Box Blog
Here's a list of all their promotions;