S30V is *potentially* a higher performance steel than AUS-8. But whether it will perform to its fullest potential depends on the heat treatment. This goes for all steels. If the heat treatment is absolutely right it will bring out the best properties in steel. If not, even a very high grade steel will perform worse than a mediocre one that has been heat treated correctly.

Then there are other factors. If the blade is tempered to a higher hardness (say, 59-62HRC) it will take and hold a better edge but it might become fragile and possibly chip when stressed. Tempering it on the soft side (55-57HRc) will made the blade tougher and capable of taking more stress without breaking, but the edge holding properties will suffer considerably.

This is directly related to blade length and profile. A shorter blade may be tempered harder as it is less likely to break simply because there is less leverage. A longer blade, especially one made for chopping, should be tempered softer. As for blade profile, a thicker bevel is going to be stronger than a thin one (self explanatory). But what a lot of people don't realize is that a blade made of properly heat treated high performance steel can be ground significantly thinner without the risk of breaking or chipping during use while it will also cut a lot better because it meets less resistance in the cutting medium than a thicker blade.

Stainless steels vary a great deal. Many are less than ideal for heavy duty cutlery. Virtually all have the tendency to chip or break much more easily than low alloyed carbon steels such as 5160, L7 or even 1095 and W2. Hence stainless is generally not a good choice for longer blades. Personally I would consider 440C to be the minimum for a good blade. 420 in all forms is not acceptable for a serious utility blade. I would avoid AUS-6 but AUS-8 should be ok. S30V should be better but I don't have any experience with it. 154CM and VG-10 are very good steels, too. But again, it depends on other factors as noted (edge profile and heat treatment).

All common cutlery steels can be sharpened fairly easily once you get to know them more intimately, though some are more finnicky than others and some just won't take such a fine edge because their grain structure is coarser. But you have to pick the right tool for the job. Water stones are less than perfect for stainless. Synthetic stones are generally ok. One cheap and quite effective solution is sandpaper (lubricate with oil rather than water for best results). Of course a diamond sharpener will work on the hardest stainless.