I don't know where to start??? Kershaw knives are not bad at all but they are not up to par with Benchmade or the Spyderco knives. I have a few of each brand in question and I carry a Kershaw Leek quite often however Benchmade and Spyderco tend to use better steel (at least in the higher priced models).
As for steel every real knife guy knows it is in the heat treat not the steel. I like D2 best so far and will not buy any 440/420/AUS6A stuff any more. A2 and 51600 is good stuff if heat treated right. Spyderco has used some steel I have no knowledge of. G10 for one Spydy's are made in Japan and perhaps other places as well, so they have steel (or at least steel names I am not up on ) that I do not know. Some may not even know 154cm is almost the same as ATS34 (it's a vacuum thang). For me I find the Spideys round hole easier to open than some oval shapes. I do like the AXIS lock Benchmade uses. If I had to pick just one knife company I would pick Benchmade how ever I do not have to pick just one so I can stay happy with all 3 you asked about.