As previously stated Magnacut is the latest and said to be the greatest. I have not gotten my hands on any yet to beat around.
I am far from an expert in this so I can only speak from my own experience.
S30V was a huge step in SS for me. I was used to 440C and Aus8 or something like that. Spyderco's S30V absolutely blows those out of the water. It literally changed my life, haha!
The next step up from that was when I bought a used fixed blade in 20cv. It was so nice not to have to sharpen once or twice a week, or more depending on what I am doing. I have since bought a bunch of knives in Elmax, LC200N and I still prefer 20cv or m390 and between 20cv and m390 I prefer m390. I know people say they are "the same" but m390 seems to be a little more flexible or soft if I can use those terms to describe it.
As to non-stainless steels. 5160 is my favorite with Delta3v in close second. I like 5160 in thicker edged big blades and Delta3v for middle sized slicey blades.