Golovkin is way better , so many levels higher. Currently Golovkin is almost unmatched. Also he beat Canelo by at least 4 rounds , so lets no go there..
I like Spence more. But he's showed nothing to suggest he's done anything of note compared to GGG yet. Compare their fights with Brook.
I think GGG, just. Im a big fan of both but think Golovkin is a little bit more polished and Spence can be a bit raw. Also Golovkin is much more heavy handed. Spence can put plenty of meat on his power shots but Golovkin seems to have some real meat on all his shots, even his jab rattles you.