Deep Purple and Led Zepplin are, of course, two of the founding father of metuhl. However, Purple ain't part of this; Rainbow is.
Both these songs are sort of long, right? And somewhat Eastern in flair. That is, I don't really know; I've heard Kashmir (everyone has). I've never heard that album Rainbow Rising, but I do own a live album. In fact, it's my only Rainbow album. Live in Churmany or something. And the version that is pretty keen.
So I'd reckon I'd say the Rainbow song for me. Yeah, pretty sweet. Overlong? Maybe. But so's Kashmir, and Kashmir don't got Blackmore, who kicks Page (no offense) to Mordor and back.
And, should this need be moved since these lads am butte prog-gressive-relations, yeah. That's kewl.