Superman. Though obviously not when it comes to magical attacks.
__________________ Chicken Boo, what's the matter with you? You don't act like the other chickens do. You wear a disguise to look like human guys, but you're not a man you're a Chicken Boo.
Golden Age Marvel family's best durability feat is flying to a zone outside the multiverse, called Infinity.
It was literally just a black void, with nothing in it, because nothing can exist there. Dr. Sivanna couldn't find any way to hurt them before, and thought that would finally be what would destroy them.
Turns out they were totally fine there, and were reaffirmed to be indestructible.
I'm not as well versed in PC Supes' durability feats, but that's the best for the Marvel fam.
Superman slams into Spectre head-first at what can be described as the utmost speeds [capable of breaking the bonds of infinity], ricocheting him back through those same infinite barries, then he gets up as if nothing happened.
That's true Invulnerability.
__________________
“Perhaps this is the ultimate freedom. The freedom to leave.”
He misses you too. Unfortunately he's going to show you how much he misses you via making sure you never experience any actual success or happiness in life. That's how PC Supes rolls when it comes to his friends.
No matter what happens if he offers to set you up on a "date" just say no.
__________________ Chicken Boo, what's the matter with you? You don't act like the other chickens do. You wear a disguise to look like human guys, but you're not a man you're a Chicken Boo.
Probably around the same physically although Supes has better feats, he fluctuates a lot more than Billy does. Of course Billy should have much better resistance to magic.
Superman has appeared in hundreds(?) more comics than Billy. Obviously his feats(in pretty much all areas that matter) are going to be better.
From an in-universe POV, however, they're roughly equal across the board... Though Superman will almost always be given the nod, given his 'status' within DC. /shrug