The main problem with solutions other than Dropbox and iCloud (e.g., Box, Copy.com,Evernote, Google Drive, Microsoft Cloud Drive) is lackluster support from 3rd party iOS apps. To me, it really doesn't matter how much storage these cloud services offer if apps that I prefer to use don't support them.
Having said that, it is very clear that Dropbox's pricing is dramatically higher than its peers. Dropbox's
CEO commented last week at Re/code that won't be cutting price nor increase storage capacity, which sounds like a big gamble.