Eh, they are interchangeable really, but I'm more familiar with Snidely Whiplash being used in pop culture references. To me, Snidely Whiplash, at least as he is used in common pop culture reference today is "An over the top, unbelievable villain who is evil as to be comical." And that is Thrawn to me. So either comparison works.

I just still don't want to see the ghost fly circles around him because they're the main characters...

They've proven they know how to make the characters fail with competent villains...

Darth Vader absolutely schooled them every time they were up against him in season 2.

And it was totally awesome.