I'm still tossing up between the 16-35mm f4 and the Tokina 16-28mm. My hesitation is mainly around NOT using a Canon L series lens but the reviews on Photozone concluded:
"Technically the Tokina is superior to the current Canon EF zoom lenses in basically all the analysed image aspects!"
These guys rate the Canon f4 over the 2.8, and only are unsure if the Tokina is much better because of quality control.
Anyone have real life experience with the Tokina?