It's a trade-off.
With Google, you probably get better security, but also the increased mining of your personal stuff by Google itself.
With Yahoo, you, of course, are all too vulnerable to hackers, but you also get a provider via a corporation of overwhelming incompetence.
It's hard to believe that such a train-wreck of an operation could be doing much successful mining of its own clients.
Pretty much boils down to this question: Do you want your personal information stolen by outsiders or by your provider?