I currently have a M&P40c, I sold my CS40 to purchase the M&P. I can't say that the CS40 was a bad pistol, it just wasn't my cup of tea. It fit my hand OK, it shot well and recoil wasn't much different than any of my orther 3rd generation 40 pistols.
One of my favoirite pistols is the PC Shorty 40, I compared the CS40 to the Shorty 40 and what I found was that the Shorty 40 was smaller in every aspect except grip width being a double stack pistol. The slide on the CS40 was huge compared to the Shorty 40, which was the primary complaint I had with the CS. The bottom line was that the Shorty 40 is more concealable for me than the CS.
When I purchased the CS I was looking for a pistol that would be small/light enough to wear in an ankle holster. The M&PC I purchased earlier this year fits the bill nicely, it replaced a M60 that I was wearing daily in an Ankle Glove.
I prefer the M&P40C to the CS40 by a long shot, if I was looking for a concealable single stack 40 I would start looking for a 4040PD. The frame/slide made the CS40 a no go proposition for me. The 4040PD is the same size as the 3913, it's a very concealable package.
When Smith started building the 40 pistols on 45 series frames they lost appeal for me. The idea of the 40 to me always has been to have a small package, i.e. 9mm frame size such as the 3913 or 6906.
Cheers,
Sam