Superman cracked his jaw, and broke him, in the Superman/Batman series. I'm pretty sure that Thanos can hit harder than Superman, and his durability allowed him from being crushed into sub-atomic particles by a black hole. Stardust and Beta Ray Bill couldn't survive such an event, so I'm thinking that he could survive Darkseids assaults, with his shields coupled with his natural body armor.
In a Physical match up, I'm also going with Thanos on this one. This is just my opinion.
It's more complicated than that, as of Final Crisis.
They're all FRAGMENTS of the same Darkseid, one that we've never seen in 'full glory', one whose presence caused the collapse the physical DC Multiverse in "Final Crisis".
And this version was that powerful because he had a special suit that made him that powerful, not because of his own inherent abilities.
Actually, it's a genius retcon that allows every appearance of the New God to be 'in continuity' without degrading the characters, explaining the contradictions and inaccuracies that have plagued the character since Kirby left.