Definitely Zelda or Final Fantasy. I think I could design an amazing old-school themed FF with great characters, combat, locations, theme, setting and story. And I would hire some amazing Japanese composers to do the music. I can almost taste how awesome it would be.
If I could live the dream of being in control of Zelda, I'd build a trilogy of titles, each one with a different theme base on a piece of the triforce. Link would travel through time in the series with one title being a boy, one an older man and one a mature hero. There would be a cool steampunkish future, a classic-Zelda styled past and a very polished HD-visual present to explore. Awesome gadgets, fast combat, unique settings, various towns, new monsters and enemies and new music would be featured throughout. That would be so much fun.
