Hang in there, FF!
D2 is a tool steel, very close to a high speed tool steel, but plenty tough for the knife application. Very stain resistent for a carbon. It's one of the best carbon steels. Plain and simple. Not a stainless, so it needs care, but aside from that it's hard to fault.
ATS34 is a high carbon stainless, same as 154cm. Excellent stainless, but not stain free. Performs close to high carbon, with the low maintenance of stainless. One of the best general purose knife stainlesses.
Both are top drawer knife steels. The 'best' is debatable, but these two are right up there for general purpose.