This is my experience so far with the aforementioned programs:

Inkscape is a very good vector graphics program, and it is able to replace Illustrator for me.

Gimp is “good enough” for pretty much anything, but the user interface is a bit dodgy and some features that I’d sometimes wish I had aren’t in it, like a layer effects stack and a more advanced text tool (although the developers are working on both those things)

I haven’t used Scribus myself yet, but my friend (who does DTP) says that the current version of Scribus is rather slow and has some annoying small bugs. He went back to InDesign.

Anyway, I hope you can find your way in linux land there’s a lot of good stuff to find, but also a lot of junk good luck.