I am not a knife maker or a metallurgist. This is my own summary of what I have learned about knife steels. You can read about this topic at great length. Lots of people who don't know tell you what they have heard from other people who don't know.
One thing is certain. Proper heat treating is as important as the steel itself. All that most folks can do is to select a manufacturer with a good reputation and trust that they have people who know how to get this done right. The design and manufacture of the knife is almost certainly more important than what steel the blade is made from.
What is the best knife steel? Why, S30V of course. This is almost an honest answer, the real answer is that "it depends". S30V offers an excellent balance of toughness and edge holding hardness. it has also been around a long time, people know how to work with it and get the best out of it. It is well proven. S30V is the steel to reference all others to. For a folding knife, S30V is ideal, other steels are good and there are some new steels that may be better. I consider S30V as the first of the "super steels.
Note that the "super steels" with high vanadium content hold their edge very well, but are correspondingly a real task to sharpen. It is best with them (and with any knife) to keep them sharp rather than let them get dull and then try to get them sharp again. It has been said that S90V and S110V are almost impossible to sharpen.
I classify steels into the following categories.
So you face a conundrum. Do you want an affordable steel that you can sharpen well (but need to sharpen more often). Or do you want a hard to sharpen steel that because you are unable to sharpen it, actually gives you a poorer but long lasting edge? The truth is that many people without advanced sharpening skills may actually be better served by a steel in this class than one of the super steels.
S35V is S30V with some niobium added. This makes it easier to machine, but is not especially better than S30V for the end user.
The thing about S30V is that it has been around a long time, is well understood so you can feel confident that people know how to properly heat treat it. S30V seems to loose a fine edge quickly, then keep an excellent working edge forever.
Note that the numbers in the S-series indicate the percentage of vanadium. S30V has 3 percent. S90V has 9 percent. S110V has only 9 percent though.
Also note that S30V is tougher and easier to sharpen (but not easy) than S90V or S110V. What you get with S110V is superior edge holding.
Note also that many pocket knives get hardened to 60 HRC or so.
Tom's Knife Info / email@example.com