Whatever works for you.
I own and use both Macs, Dells, BOXX and HP for film, CG and motion design.
I would love to get a tricked out iMac but without a decent display pairing, I can't justify it.
At home and work, we run the D700 fully loaded and they are doing fine with each OS and Adobe updates.
My PCs are mostly for Maya and the odd Resolve/Avid project.
Again whatever works for you.
If you need one today then make sure the iMac will deliver.
If you can wait till the new year do so and wait for all the reviews.
The systems below have10 Core CPU as opposed to the base price 8 Core iMac Pro. One has a GTX 1080 and the other the GTX 1080 Ti. I would prefer a 21:9 aspect ratio for the monitor for Premiere Pro but some programs work better with the 16:9 aspect ratio. The iMac Pro looks like a beast until you check out the Windows 10 PCs.