For me it’d have to be Jonny Greenwood of Radiohead. He could throw in some off-the-wall orchestration, a bit of his idiosyncratic guitar playing or a smattering of electronic flourishes. Listening to Thom York’s solo records makes it clear just how much Jonny brings to the table in my opinion - he’s the kind of musician every band or artist would benefit from.
Who would you choose?
) I just know 
would emerge