I think there are two kinds of "reliability" getting conflated here. There's reliability as in "this is built on the stable foundation of a big system and has a bunch of engineers ensuring it's Highly Available" -- both Google and Dropbox can give you that. Then there's reliability as in "this product won't blow away in the corporate-political wind" -- and Dropbox is the only one who can truly say that. (Though Google Drive is pretty core to a lot of stuff Google does, e.g. Android, so it's probably not going anywhere either.)