I would avoid Google Apps for Business as your primary storage solution. When I was sourcing alternatives, Box.com was the only one that I felt would provide some benefit. In the end, I didn't see enough of an advantage to offset having to spend agonizing weeks migrating our files. Also, it is a lot more expensive; you get what you pay for.
My advice is based on the following reasons, and the company I work with is similar in size to your own. Also, please keep in mind that the grievances listed are based on my own experience. There could very well be solutions to these problems that I am not aware of.
Pooled storage is not available. Each user is allotted 30 GB of space with the option to purchase more when needed. The work-around we used for this was to designate a single user account as the "owner" of the majority of our files, and transfer all files to that user when a staff member hit their data cap.
Only the owner of a file or folder can delete it. In testing and daily usage, I have found this one to be hit-and-miss. Deleting a file that you do not own simply "unsubscribes" you from viewing that file on your account. All other users can still see that file, and this is apparently the intended functionality. At times, it appears that I have actually successfully deleted a file that I did not own, but I have been told that this is a bug. If the owner of a folder deletes it, all files within that folder owned by other users are orphaned, not deleted. Orphaned files quickly accumulate in this fashion and it compromise the effectiveness of future searches.
There is no root/administrator account. Administrators' capabilities within Google Drive are the same as the common user. Admins are unable to take action on a file/folder on behalf of the owner, nor can they change permissions on files owned by other users. A tool exists in the administrative console to allow for the transfer of ownership of all files from one user to another. This is helpful, but usually requires you to run the process several times, as ownership transfer errors are fairly common.
There are only 3 permission settings for users; can view, can edit, is owner. This very restrictive, especially when you consider that those with edit permissions can change the permissions of their fellow editors. Google does allow for the construction of permission groups.
The interface is slow to load if you have a complex file hierarchy. Large folder trees take multiple browser refreshes and complete minutes to load in their entirety. Unfortunately, while this loading is taking place, the browser is essentially unresponsive. To Drive's credit, it performs much better on my home machine, but the reality of the workplace is such that users are generally not enjoying the pinnacle of computer hardware at any given time.
Although Google provides a "breadcrumb" bar, it is evident that the system relies on a parent/child structure. When searching drive, grey and bold text indicate which folder a particular file resides in. Unfortunately, it only displays the parent folder. In the event that you have multiple folders with the same name, good luck figuring out which one it is in. Also, when using the "Move to" dialog, it is difficult to assess where a file is currently located as the dialog opens with a collapsed view of the root folder. If the file you are looking at is in a sub folder, start digging.
The UI "preview" overlay is the default action when a file is left-clicked, and this cannot be disabled. I chalk this up as "nit picky," but there is a stickied complaint posted in the Google Drive product forums about it, so I'm confident that there are others sharing in my agony.
Trying to get your files out of Google Drive is difficult. There is a batch process, which I have only attempted once, and it resulted in failure. Good luck leaving Google Drive if you've committed to it. It sound easy, but my experience suggests otherwise.
That said, there are several advantages. A few are as follows:
I love Google Docs. Docs will make you begin to think about abandoning Microsoft Office. There are a few power features you will lose like VBA macro programming, mail merge, and a lot of flexibility in formatting. But, when you consider that you can actively collaborate with other users in your organization in a browser window and track each others changes, you long for the days when it is a full replacement.
Static linking to files. I know this is pretty common in the cloud storage space, but it bears mentioning. There is nothing that makes me happier that clicking a link that takes me directly to a share a la windows network hyperlinks (\share\myfolder\mydoc.txt).
If you have enough time on your hands, you can symbolically link files in multiple places. Simply control+click multiple folders when choosing to "move" the file. This is a bit cumbersome, however, and the interface is not very efficient.
It's cheap. Literally nothing comes close to the power you glean from a Google Apps for Business subscription. It is far-and-away the most cost effective cloud business platform from my vantage point.
Google Apps API. If you fancy yourself a web programmer, there is a sophisticated API that allows you to programmatically interface with Google Apps. For most smaller companies you may want to hire a programmer (not cheap these days) or start wrapping your head around OAuth2.0. I'm currently working on a script to allow me to extract static URLs to all folders so that I may import them as shortcuts in another app.
Sadly, the list of drawbacks I provided is the short list; these are just the ones that came to mind. But, Google is always making updates to improve functionality. You have to remember that you are seemingly commiting to a service which is still very much in its infancy. More importantly, Google is designing Apps to work for many market segments - businesses, consumers, education, and government - so development priorities consider all 4 groups, not business customers exclusively.