I'd be using the lens for landscapes and architecture.
I have filters on all my lenses currently, but I'm not opposed to the bulbous front end of the Tokina. I'm very careful and I am sure I can make do without a filter.
Thanks for your reply.
The thing that is so tempting about the 17-40mm is that, as you have pointed out, it is quite cheap for an L lens. I can buy a good used copy and invest the rest of the money saved into something else I like. The Tokina is about $200-300 more expensive.
I think that would be the most important consideration for me. If it were not for the bulbous front element, I'd be the proud owner of the Tokina today. I didn't love the sharpness of the 17-40 and sold it- on the other hand the Tokina was very good.
There are filters for Tokina. See here: