I have seen videos of an aluminum frame snapping at the weld where the front vertical shaft (where the fork is mounted to) shears off the two horizontal/crossbars. Though these people were doing lots of big jumps on their mountain bikes.
I think you will have issues with snapping in either case. A number of factors come into play here. Material quality (mixtures, purities, impurties, etc), how the material was formed (die-cast, poured, laser metal sintering, etc), the quality of the welds or glues that hold it together (I am assuming they use some form of gluing for carbon fiber), material thickness, construction design, and a few other factors.
The biggest benefit you get from either material over steel is low weight, with carbon fiber being the lightest by far. The next benefit is corrosion/rusting. Aluminum doesn't rust. But it can be corroded. Carbon fiber isn't a metal, so rusting has no possibility. But I would think that it would be more sensitive to acids and bases when it comes to corrosion.
Steels biggest advantage is flexibility, it will bend a lot more before it breaks.
I have been using aluminum bikes as of recently and they are plenty light for me for my mountain biking. I don't do any big jumps (at this point). So I don't know how it would hold up for that. But I can see it holding up pretty well.
And if I were doing a bunch of jumps I would want something with enough heft that I could more easily keep it under me. I would be worried that carbon fiber would be so light weight that I could lose it to a stiff wind while in mid air if I loosen my grip too much.
I will say this. Those carbon fiber road bikes are freaking sweet. I never thought I would be able to pickup a bicycle with one finger until I saw one of those.