I am looking for advice on which one to get for full frame. My quick history is that I have always been shooting primes (35-50 primes) and I would say that I'm an advanced enthusiast, with my favorite photography being Nature/Hiking, Landscape, Nightscape/Astro (Long Exposure), Street, Food.
I use an 80-200 f/2.8L for Portraits and Landscapes/Nightscapes, 35 f/2 Non-IS and 50 1.8 STM for Street, and recently just picked up a 24-70 f/2.8L II for Hiking/Nature.
I use a Canon 6D (after my 5DC, I can't go back to Crop Sensors) so the images would be true to the 35mm size.
Overall, I have been reading a lot and the f/4L IS looks like it's Canon's sharpest ultrawide zoom, but I always tend to buy lenses with apertures f/2.8 or less since I want to have the option to shoot handheld in the city at night or just in general when it's darker, but it looks like everyone's saying to go for the f/4 since it's a better bang for the buck and it's cheaper ($725-800?) while the f/2.8L II is a little more expensive ($850+).
My goal for the lens would be for occasional Astro photos and startrails and also just general purpose.
Please let me know what you think, thanks!