omg too hard to decide. one of my favorite foods is potato salad w/ egg in it. they're both so versatile:
potatoes - french fries, chips, baked potato, hashbrowns, mashed potatoes...
eggs - scrambled, boiled, poached, and an ingredient in so many other recipes (cakes, mayo, etc)
I looooooooove potatoes, but I think I'm gonna have to go with eggs for the win for their versatility.
What about you?