Jones is right, there's quite a bit of controversy about the testing of this caliber. Generally disregard any testing done by the company trying to sell you ammo, as well as fanboiz who have no experience. When a bunch of people have shot bad guys with it and dumped it for an AR (which they then found acceptable) it sends a pretty good message. The 5.7 can and will kill people dead, so can a .22LR, .380, and many other calibers. A pistol caliber is a compromise in the extreme, and should never ever be used when a rifle caliber can be. You're kinda sorta taking a 5.56 nato and cutting it in half.
If you are just dead set on the 5.7 (and it's a cool little round), I'd go with whichever is cheaper (pistol vs. carbine) and spend the rest on training and practice.