3 stand out in my book for fixed blade steel:
1) INFI: tough as hell, never gets so dull you can't use it. Against soft materials the edge will last a very long time. Against hard materials... ditto. Virtually stainless (more so than D2). Not invincible, but as close as I've seen to it.
2) CPM-3V: Can't speak for all makers heat treatments, but Fehrman gets it right. It's incredibly tough stuff and very wear resistant. Takes a better edge than INFI, but doesn't hold it quite as long under the same usage IMO.
3)SR-101: Busse's heat treatment applied to 52100. Very similar in performance to CPM3V, but easier to sharpen. It is, however more prone to rust than the other two. For the money, it may be the best value in a fixed blade today.