Pie. Cake is good, and in fact some cakes are great, but most common cakes are only good in small quantities. On the other side, there are plenty of common pies that are delicious enough to require multiple servings.
What.
I can eat a whole damn cake all by myself. Can, and have!
Cake all the way!
Seconded. Hell, I've eaten entire cakes by myself in one sitting. Smaller ones granted, but I'm counting them.
I'd go with cake. Given the opportunity, I would eat cake every day, whereas I'll only eat pie at holiday meals, and then only a single, smallish piece. And only if no one has made cake.