With the exception of corrosion resistance, I find M2 to be better for me in every respect than 154CM for a folder of this class. It is harder and thus stronger. As tool steel, it is also it is also tougher than high carbon stainless steel, even at the increased hardness level. I can't (actually won't) qote some charpy value, since that is pretty meaningless to me. Instead I can tell you I have used my M2 knives without damage where ATS34 blades were dulled either by edge roll or micro-chipping.
But edge holding is not why I prefer M2. Instead, it is because that extra durability allows me to have a thinner edge at the same level of durability. So I can have my cake and eat it too, so to speak. Joe Talmadge has explained this so many times over the years that all I could do is echo him, seek out his posts and you shall have your answer about how better steel leads to better performance.
Here are some M2 Benchmade pics just for the heck of it:
730 Ares
710HS:
Of course, if you place a premium on corrosion resistance or shiny metal, then the 154CM may be better for you.
As well, consider that much of what is written about steel should be taken with a grain of salt, yeah even what I just wrote. People use knives with "inferior" steels all the time to good effect. The people that use knives the hardest don't even know what steel there knife has, nor would they care.
Even if you use your folder is destined for hard use, 154CM will do just fine. My brother is harder on knives than even OwenM. He has broken every folder I have given him, several Kershaw and Spyderco FRN fodlers for example. For almost two years (give or take) he has been carrying a G10/154CM Axis lock and it has survived. Yeah, the tip has been snapped off a couple times and I have put thicker tips on, and it has been reground a couple times, about it has not suffered gross failure (blade snapping, handle failure, busted lock) as the other have.
Butthat is just my opinion. It is probablly worth what you paid for it. . .