Discovered I need a wide angle this weekend

As I have been told " you will know when you need something new". Well I discovered I need to get a wide angle lens. I was using my 5D Mkii with the 24-105mm and I discovered I needed to go wider. So, now the question. What wide angle lens is best for the 5d mkii? I would prefer not using a prime lens as sometimes I need to go a little wider or zoom in and would rather not to have to take the time ans switch lenses. I have been looking at the Canon EF 16-35mm f/2.8 L II USM Lens. I did not know if there was a better one by canon or by a different manufacturer. Any suggestions?