16-35mm f2.8 or f4?

I have the 16-35 F4L IS. You can shoot it up to and after sunset handheld at 1/10. Sometimes its nice to not be tethered to the tripod.

I wound up with the f/4 IS lens.

I also shoot video, and IS is vital for DSLR video if it's going to spend any time off tripod.

I don't do astro, but my understanding is that the f/4 lens has much better coma correction, and that's important in astro (stars off-axis remain points instead of turning into streaks).

I stuck to the Canon lenses rather than the Tamron because the Canon lenses use my 77mm filters.

I've never noticed coma shooting at F4 on my 16-35 f4.

I ended up going with the f/4. Couldn't be happier.