I'll back up a bit...What does the op mean by "stronger"?
Both guns are available in the same calibers. Both have 5 shot versions in 454 Casull and other powerful calibers. So it comes down to specific design features.
If, by stronger, the op means which is less likely to have a catastrophic blow out of the cylinder and top strap due to an overpressure handload than it might be the Super Redhawk. This due to the design of the frame. Though that doesn't account for the cylinder which is most likely to blow.
If we are talking about the durability of the gun, the ability to shoot thousands of rounds of powerful loads without mechanical fault. Then it's probably the Super Blackhawk. The single action is a simpler and stronger design than any da gun.
But this is a gun forum theoretical question mostly. Meaning that it's a good question for nit pickers and folks who worry too much that their guns will blow up. Either of these guns in good condition will meet any shooters needs for longer than their elbow and wrist joints will hold up. It's mostly a guess as to which is "stronger" because you'd have to purposely abuse the gun, repeatedly, to find out.
In what caliber?
Which do you shoot better? Which carries better? For what purpose is the gun? Those questions are likely more important for most.
tipoc