If I start doing all my work using google apps.... I go from hard drive dependent to google dependent? I could access my files from any computer. Not sure, though.
I like dropbox. I use google drive for some things that I want to share with others. Otherwise dropbox lets me save documents that I can open on my other computer or my phone.
I use both dropbox and google drive, I can't say I have noticed any real difference between the two in terms of features that I use. I just tend to keep different categories of files and data separated. One nice thing I did stumble upon that's pretty useful was uploading all of my music files into the google "play music" cloud so I can stream them to my android phone.