If you're shooting a wedding with one camera, get the 16-35 so you aren't stuck super-wide until you can take a moment to change lenses, and that'll leave a little budget to buy a second camera.

If you want great image quality and can spare the budget, take a look at the Zeiss 15mm 2.8. I've really enjoyed shooting with it when I rented it, and the micro-contrast is out of this world.