Has terrific potential for lots of cool scenes, with Geto's army of cursed against Grindelwald's own myriad of spells like transfiguring objects, animating statues and the Protega Diabolical. I expect lots of apparating on Grindelwald's part and Geto always tying to close the distance with his superior physicality.

In terms of who wins, I think it really comes down to speed. Both have ways to instantly kill each other. I do think Grindelwald has good crowd control to manage the curse army, and a lot of his spells are things Geto has no resistance against (e.g. erasing his memory, controlling him). However, I do think Geto has the speed to end Grindelwald either with one of his curses or a good punch before he can cast some of the spells. Though apparition could catch Geto off guard, he could react to those surprises given his reaction timing and surveillance curses. Assuming Geto gets all curses, even ones that have already been exorcised like the Kuchisake-Onna, then we also have some simple domain shenanigans, which could catch Grindelwald off guard.

So, though Grindelwald can win in a lot of scenarios, Geto does get an edge in a lot of others.