Who the hell can afford to go to either one? A "value meal" at McDonald's is nearly as much as a fucking steak dinner. I know which one I'd rather have.
Starbucks coffee is crap, but few people actually drink coffee there. Where they make their money is on the sweet, sugary drink concoctions that occasionally contain coffee. With a little time and effort, you can brew coffee - and even Expresso - for much, much less than you pay for it at Starbucks. And your end product will be much higher quality.
I haven't eaten at a McDonalds in years. They're in the coffee business now too, probably with the same results as Starbucks.