As much as i hate repaints i justify it like this. Gen1 was full of repaints: Bumblebee/Cliffjumper, Prowl/Bluestreak and all the seekers. Therefore repaints that represent a character from Gen1 are ok but repaints for the sake of repaints are bad.

I say: Buy both. Darkmount is a character from the comic that has never been released before and Skullgrin is cool, and a release of an original Gen1 character. It's justified. They can be displayed differently weapon wise and even cleverly transformed.