What body are you using? I ask because you mention 10mm, and if you can use a 10mm lens on your body, I expect you have an APS-C camera.
The 16-35mm f/2.8L II is an excellent lens, and I enjoy using it on my 5DII. But if you have a 1.6x body, 16mm is wide, but not ultrawide. If you want ultrawide, get a Canon 10-22mm, Tokina 11-16mm, or Sigma 8-16mm. If you want -'wide-to-normal' like the 16-35mm f/2.8 offers, get the EF-S 17-55mm f/2.8 IS instead - it's cheaper, has IS, and will yield better IQ (except for vignetting) than the 16-35mm on APS-C.
If you have a FF body (or APS-H), let us know - that makes a huge difference in lens choice!