My everyday use/abuse work knife was a delica 98 in ATS55. I was very happy with that steel. It never chipped on me. And you could sharpen it to a very thin edge without to much worry about it rolling on you. It wasn't the easiest in the world to sharpen, once it was dull it took a long time, not to bad to touch up about once a week on a ceramic stone.
I just recently got a benchmade 750 (in ATS34) to replace the delica. I haven't had a whole lot of time to test it yet. But it takes a good edge ( after you thin down those Axe grinds that benchmade puts on it
) And it seems to hold it decently, but like I said, I haven't had a chance to really test it. It did take a long time to reprofile the edge which gives the impression of it being very wear resistant.
As for which is better... ATS55 is a steel specifically designed for cutlery. It is a modified version of ATS34 which is a tool steel, probably used more often on knives than in tooling. But anyway, The ATS34 has a little more carbon, less chrome, and less of the other elements that go into the alloy. The ATS55 will probably perform a little bit better due to the fine tuning of what goes into the alloy, and since it relies on things like molybednum ,vanadium, yadda yada yadda, instead of carbon to make it perform, it should be more resistant to corrosian.
Either one makes a good knife though.
It'll feel better when it stops hurting.