I personaly would probaly vote Universe Ultra Silverbolt, as a recent example of a major fail, he and Galvatron should swap size classes.

That said All the toys mentioned, have at least one redeeming feature though, i.e Spinning top Prime, has that awesome rifle accssesorie so he's not a complete failure. Galvatron too for all his failings still had a nice G1 Galavatron head sculpt, I suppose that cursed Silverbolt does too. Devestator has his nomm nomm feature so they all seem to have one redeeming quality which to me keeps them form making absolute worst toy status.

So after thinking about it I think I'd have to go with the afforementioned Supreme Cheetor toy, he's big, ugly, exspenisve, and stupid what an amazing combo.