I use a combination of box, dropbox, Onedrive, Copy and of course Google Drive.
To be honest, dropbox is probably the best out there at the moment (especially when you are syncing large volumes of data), but unless you are willing to pay, or have a lot of referrals, it is limited. I have two 50GB box accounts (one that Titanium Backup auto backs up to, and one for other stuff), Google Drive for G+ photo/video backups, Onedrive (with 100GB promotion for 2 years + 25GB standard from my old account) for random transfers to/from people, and for documents backup between my computers/phones/tablets, and Copy gets a backup of everything (redundancy).
I stopped using dropbox after they, out of the blue, decided that 15 or so of my referrals were "fake" and didn't provide any explanation of why those were fake. I know some people were using fiverr to get fake referrals, but the folks I referred were actual friends (students), that are actually using those accounts even now. They signed up within a span of 4-5 days, so I guess dropbox tech team thought those were fake. Anyway, I stopped using them after that.