I use the $2,000+ 17TS-E almost every day, it is lauded as the best ultra wide lens made by Canon, I recently got a new 16-35 f4 IS for $999. At 17mm the zoom has every bit as much resolution as my TS-E and the contrast is much better.
The 16-35 f4 IS is a very very good lens with sharpness and contrast that rivals the very best available, throw in IS, the 77mm filter thread, and the keen price, I am more than happy with the purchase.
i will be getting the 17TSE I know its a super good glass but since you own it is the 16-35 f4 a better buy. I will not be switching a prime for a zoom thou.
They are very different lenses that do different jobs, but as a 17mm 'prime' the 16-35 f4 IS beats the pants off the 17TS-E. Of course if you need tilts and/or shifts then the 16-35 is useless!
After selling my 16-35 f2.8 MkI and using the 17TS-E as happily as I was I wasn't actually planning on replacing my ultrawide zoom, but after seeing it on CPW for $999 I thought I'd give it a go and I am very happy that I did, the IQ from it is staggeringly good and the functionality with the zoom, weatherproofing, AF, IS etc just makes it a supremely good package. I know it is really the 17-40 replacement, and as such it is a large cost increase, but to my mind it is worth every penny and some.
The 17TS-E does stuff the 16-35 never will, but unless you really need that functionality then the zoom is a vastly better buy. And unless you must have the 17 fov I'd recommend the 24TS-E over the 17 any day.