Apologies for the wall of text in response to simple questions, I am not trying to over-complicate it, merely trying to be comprehensive and explain my frame of reference in order to be fair to the products.
The S30V vs D2 question is beyond my ability or experience to answer for many reasons. I am not good at sharpening so when I struggle to sharpen any knife I blame my lack of skill rather than the steel. I have very little use on these AFCKs and have done no direct comparative testing of edge holding etc.
It is hard to say which one is "smoother" because I feel that people interpret "smooth" very differently. Some people interpret smooth as a blade that they can open or flick open and closed easily with little resistance. I define that as "loose", not smooth. Others interpret smooth as a lack of noise and vibration. Others define it as a consistent action under constant pressure, without jumping or slowing (also including in and out of the detent). And of course there are more criteria and different combinations of the above etc.
You can make many knives "smooth" by loosening the pivot enough to minimize jumping or slowing during the opening/closing action, reduce noise and vibration and have a weak detent to avoid jumping on initial opening etc.
I don't like free-swinging blades. I tighten all mine to the point where the blade will not move unless I pressure it to move. So I cannot flick open any of my knives, hence none of them are "loose". Although I really liked it, I sold my S90V Manix 2 because I could not tighten it enough to not swing freely.
So to me, "smooth" is a knife that is tight enough where the blade will not swing freely or move without me moving it while at the same time having very little noise or vibration during the action, move consistently with no jumping or slowing through the entire action, especially under very light pressure and most importantly, not jump too much out of the detent even though the detent has to be strong enough that the knife does not open unless I open it.
So from that perspective, I find most knives with very strong liner locks are not smooth by my definition because there is always stong pressure against the blade from the locking liner that causes noise and vibration. Each of my Militaries are different. The CF S90V one has a very strong locking liner and a very strong detent so it jumps on opening and it is noisy but the action is consistent. The S30V one has a weaker locking liner so it jumps, but not as much as the S90V one. It is less noisy with less vibration but the action is less consistent, looser in the the beginning but tightening gradually. The M4 frame-lock version has the most noise and vibration of the 3 and a very inconsistent action under very light pressure.
The Paramilitary has a weaker detent than the PM2 and I can actually move the blade a little before the detent releases so it does not jump as much on opening as the PM2, has less vibration and less noise in the action. Both the PM and the PM 2 jump a little during the action under very light pressure. One of my 3 PM2's I cannot eliminate free-swinging from the blade when the lock is released but it is less of an issue because with the compression lock design there are no fingers in the way when releasing the lock.
One of the reasons I like the Spyderhole is that you do not lose contact with the hole when the blade jumps out of the detent. I had a Bradley Alias that jumped out too much and every time my thumb lost contact with the thumbstud and came down on the blade near the cutting edge. I sold it.
To me, Axis lock knives generally have less noise and vibration than liner and frame locks because of the mechanism of its lock, Axis lock knives generally have consistent actions but they have that funky jump shortly after overcoming the pressure of the Axis lock that keeps the knife closed. And on closing it is inconsistent when it has to overcome that pressure to lock it closed, and then jumps closed after it does.
The AFCK hole is chamfered and the Spyderhole is not. When I first got into knives I guess I was like you where I used to sit there and open and close them continually and on some other models I did notice some hairline cuts on my fingers but I have not experienced that in a long time but I don't have those knives anymore and I don't open and close them continually anymore.
The only folders that I currently own that I consider smooth are the Sebenza, Umnumzaan and the liner lock, round hole AFCKs. I am sure there are many others too that I have not experienced yet. But that will differ for everybody and many consider all these knives under discussion as very smooth. There is no right or wrong, just different interpretations of smooth.
But I want to emphasize that these are all things that are only evident if you look for them, i.e. opening the blade very slowly, with very light pressure, ears pitched listening for any sign of noise. They are not things that I notice during regular use. All these are among my favorite knives.
Thanks for the good words!
