Someone else has already asked, but I'll ask too: What are you gonna cut or chop with a tomahawk?
Personnaly I see them as decorative more than anything else, so as far as I'm concerned, the blades could be aluminum. I'm not gonna chop wood log with a tomahawk (I've got an axe for that), and I'm not gonna prepare dinner with it either (I got knifes for that). In 2016, tomahawk are used either in tomahak throwing competition (which I wouldn't even know how to enter such a compretition), or as a jack-of-all-trade tool, used as a prybar, a smashing tool, or even a bottle opener (which partially explain why eveyone in this thread wants this or that feature). It might very well be the best case of solution looking for a problem (a very cool-looking solution, I'll admit). So in that case, wtf debate if this or that steel would be better? If everyone is gonna have a different usage for it, then I suggest that scrap metal would be a good enough steel for a tomahawk.
I think most people make quite a fuss about steel resistance in their cutting tools. My President's choice knife set is roughly 440A steel, which is as soft as steel gets, and those knifes can chop carrots and chicken cartilage all day long. I do need to sharpen them once in a while, but the softness makes it really quick to sharpen. Given that I have no clue what I'd do with a tomahawk in the first place, then I can come to the conclusion that the softest steel there is would be hard enough for my need.
But 5160 is cooler, cause, you know, swords.