As far as production folders go, S30V is about the best (balanced) stainless you can get these days. It is for sure the toughest stainless you can get, and holds an edge about equal to, or up to 20% better than, D2 depending on the source of info. It's plenty corrosion resistant. The new benchmark for stainless.
M2 is a very good steel for a production folder also, but is not stainless of course. It is a high carbide content tool steel (very good abrasion resistance), and Benchmade targets Rc60-62, about the hardest target range for a production folder, so it'll hold an edge about as well as anything you can get in a production folder. My hard use folders are in M2 (BM710 & 800, and also an 812). M2 is a bit tougher than most of the other abrasion resistant steels, but is probably overrated for toughness by most (I'm guilty of this in my past posts). I haven't seen a good chart that compared S30V and M2, but wouldn't be surprised if they are quite close in toughness.
Unless you are having corrosion problems with M2, I sure wouldn't dump those folders (or drop me a line if you do).
Both are high performance steels for what they are, especially in the folder arena.
Now that I think about it, S30V has come pretty close to obviating M2's niche as a premium folding knife steel. (i.e., S30V has a good fine grain, and is about as tough and abrasion resistant as M2, but is stainless. M2's only notable merit now is that BM runs it hard at Rc60-62 and most of the S30V is coming out in the Rc58-59 range, except for a few custom makers at Rc60. That, and some find it easier to get a wicked sharp edge on M2 vs. the CPM S30/60/90V steels.)
Neither is easy to sharpen unless you have diamond stones. But stuff that is easy to sharpen is almost by definition going to be easy to dull also. Word.
Here is a good thread from Sal Glesser:
http://www.bladeforums.com/forums/showthread.php?s=&threadid=270056