The manufacturer of the rings has far more bearing than the material.
Where accuracy is concerned, you likely won't see any difference between well designed rings nor what material they're made of. Perhaps a well honed benchrest shooter could tell the difference. Perhaps.
Badger, Nightforce, Seekins, Spuhr, etc....all good ring and one piece mount manufacturers. Some manufacture both steel and aluminum rings, and both materials are priced about the same, respectively.
So where does the rift between steel and aluminum occur?
Preconceptions would be my guess.
The time honored tradition of believing that steel goes on steel and aluminum goes on aluminum, because temperatures and dissimilar metals and vibrations and one is harder than the other....which seems a bit silly once you see aluminum on steel at competitions and nobody is complaining when they win. That, and the fact that the metal your scope is made of is often aluminum too. So if you're putting them together, would it be better to have aluminum scope and rings on a steel rail, or an aluminum scope with steel rings and rail? Either way, you have different metals together...so it kinda cancels the argument out.
You see steel on a lot of military DMR's and rifles of that nature, presumably because the military believes that steel rings are just tougher...not because of some magical thing that happens when you clamp different metals together.
Well, the difference in potential strength between them is apparent, though is that strength really necessary?
Few scopes will be usable after an impact has damaged aluminum rings, so the strength issue is a bit overrated.
Consider this:
Steel rings....."Your scope's ruined and totally useless, but hey....those steel rings sure held up to that 20ft drop as advertised!"
Aluminum rings...."Your scope's ruined and totally useless, and it appears that your aluminum rings got kinda ruined too after that 20ft drop."
Not dropping your rifle off a cliff...."Hey, those aluminum rings are holding just as good of a zero as my steel ones are"
Oh, and Nightforce makes great optics BTW, that actually is a good suggestion.