I would like to hear from people who have handled at least two of these steels and that can compare them as to which of these steels that can hold a sharp edge for the longest time.
S110V - These knives take and hold a good edge, but they do not feel as sharp as a lower carbide steel. You end up with a nice toothy workable edge after the shiny wears off. May be prone to micro chipping due to the higher carbide content. Good corrosion resistance, and it has some good toughness, but not great.
Spyderco Native
Spyderco Para2
ZDP - Excellent steel, holds a super sharp edge, might be some micro chipping, but it hasn't been a problem for me I keep the edge andle around 20 degrees per side with a small microbevel. At a steeped cutting edge, the chipping will be almost inevitable, depending on blade stock thickness. Blade may develop a patina or staining after a while.
Spyderco Stretch
Spyderco Endura
CTS-204P - Similar to M390 and CPM-20CV very good, well rounded steel in terms of corrosion resistance, toughness, and edge retention. Ultimately I prefer this in a larger blade for daily use. Very good corrosion resistance overall and the edge seems to stay very sharp overall, regardless of reasonable use.
ZT 0562CF
Microtech Ultratech SE
Sharpenign is relative, if you have the right equipment and have a decent understanding of what grit to start with and when to finish, as well as proper technique then none of these steels is "hard/impossible to sharpen". The people that have trouble the most are people that are illequipped for the sharpening job, lack practice, and have no rudimentary understanding of which grits and which equipment to use.