I have almost 50Gb of free Dropbox storage btw, through referrals + events like the space race. But that's not really a fair fight anyway, since (aside from Dropbox) no one offers free space in exchange for actions..
For cost comparison (UK pricing);
So, Google wins on free tier, but Apple takes it on options and cost thereafter, and 15GB arguably is still insufficient for "OS storage" in any real tangible terms.
 no I don't have data. I do know plenty of Dropbox users though, and next to none of them have any extras.