My personal experience:
M2 is easier to sharpen, and it gets sharper than ATS-34. It is <u>supposed</u> to be tougher (don't know this personally, as I've never demonstrated ATS-34's lack of toughness to myself).
I keep reading everywhere that it is supposed to rust easier (well, I can believe that), and one guy even described it as a "rust magnet." Ask me in a few months, and I'll be able to tell you for sure, because.... I sanded all the BT2 off my M2 Nimravus Cub. I have put a coat of olive oil on it, but I haven't re-applied the olive oil in about 10 days. In the meantime, I have continued to use it normally. So far, not a speck of stain or rust. To me, especially with the BT2 coating, it is definitely a better choice of steel.
"Absolute safety is for those who don't have the balls to live in the real world."