For me, I suppose the main thing is the steel and how well it holds up (so I don't have to hone so often). But our ancestors made great furniture with the chisels they had and the steel was plain carbon steel, with unknown other elements. You can do excellent work with almost any chisel, as long as you understand its strengths and weaknesses.
Some of the modern steel, such as the powdered metal steel, will hold an edge longer than plain carbon steel.
Mike