No difference between the kinds of steels but there are big differences in strengths depending on the model you are looking for. If you are considering a double action revolver then they are all the same (as in their ability to handle heavy loads) but if you are considering a single action gun and want to shoot heavy or "Ruger Only" loads occasionally then you want something from the Blackhawk or Super Blackhawk line. Even amongst Blackhawks there are now "Flat top" models which are built on the smaller "New Vaquero" or "Vaquero" frames that cannot handle heavy loads.
The current Vaqueros or as they used to be called "New Vaqueros" are built on frames closer to the size of the original Colt Peacemakers and while still strong in their own right, are not designed to shoot "Ruger Only" loads. If you want a Blackhawk just be sure it's not a flat top model built on the smaller frame and you'll be fine. The only sure way to tell a large frame from a smaller frame gun is to look at the serial number. If the prefix is a two digit number it's a large frame and strong enough for "Ruger Only" loads. If it's a three digit prefix number than it's built on the smaller "Vaquero" frame and not capable of shooting "Ruger Only" loads.
Of course this applies pretty much exclusively to the .45 Colt caliber but since you didn't mention what kind of Ruger or caliber you were looking for I thought I'd cover them all. If you are looking for a Ruger single action revolver capable of shooting hot "Ruger Only" loads, even occasionally, I'd recommend the Blackhawk Bisley. The Bisley grip frame tends to handle the recoil of heavy loads much better than the standard "plow handle" style grip frame. I have a 5.5" stainless Ruger Blackhawk Bisley .45 Colt/.45acp convertible and it's a sweet beast of a gun. I highly recommend them but I highly recommend any of the Ruger revolvers too.