I've been experimenting with both, and both work rather well for most things. It seems DropBox and Microsoft collaborated to get their apps working together, but I'd worry about other apps being supported as readily. But at least it seems like I can open and edit Word and Excel documents from DropBox, and have them save directly back to the "server" without having to forward a copy from app to app. That's nice.
Problem is, many companies (including my employer) won't allow storing files on a third-party cloud locaton. To replace PCs with iPads at my company, we'd need a way to open and save documents from/to a Windows PC shared folder. Is there a way to do that?
It does look like iOS devices can access folders shared from OSX Server at least. The option is kinda unintuitively hidden in Settings, Mail Contacts Calendars, Add Account, Other, Add OS X Server Account. They must not want anyone to ever find it, lol. Kinda neat though, especially if you have an all-Mac office.