Tough decision that one would be. On the one side you have one of the most prolific Japanese audio giant offering what appears to be a TOTL model for the mid-70's... which is also what another Japanese (formerly American but that's beside the point) brand somewhat lesser known in the field of cassette decks but highly regarded for its striking aesthetics and the sonic qualities of their iconic receivers. Never was much into cassette decks myself let alone interested in acquiring what I imagine to be pricey units for a teenager's budget in those days. I don't recall ever seeing a Marantz deck but judging from the photos seen online it was quite the looker. As for Pioneer cassette decks I have seen plenty and I find their more sober appearance somewhat reassuring, as if they had put the money at the right places and for once, that appears to be the case here, with Pioneer sparing nothing to provide their customers with both the proven and new non-gadget features (as in actually useful SQ-wise).
So for me it comes down to this: which one I would choose would entirely depend on intended purpose: listening to it or having it displayed in the music room as a conversational artefact of the golden age of two-channel audio. For listening I would go for the Pioneer otherwise it would probably be the Marantz. Not saying the Pioneer sounded better, that I don't know, but it came with a solid reputation, was feature-packed and was better known by the public this side of the world. Stalemate then? No, not at all. Since SQ and problem-free operation matter more to me than looks I would probably go for the Pioneer anyway so that's where my vote goes.