The Heckler we demoed had a lot of excellent handling characteristics. It was stable at speed and very balanced, but still dealt well with slow speed technical work. It had some of the snappiest pedaling manners and great handling of any bike I have tried recently. However it suffered some obvious stiffening under braking in the rear and the pedal feedback when climbing rough terrain was annoying, especially in the granny ring. I'm not sure I could get over the pedal feedback thing. It's too bad, the bike was great otherwise.
The Giant was a pleasant surprise. Despite an extremely unconventional look, it came together nicely as a package. Pedaling, climbing, descending, and all around it was extremely competent. Not as precise feeling as the Heckler, but it also didn't exhibit any of the negative traits the SC did. It pedaled as well out of the saddle as the Heck, but did not seem to stiffen under braking or yank at the pedals through chain feedback. Standover was excellent. The cable routing left something to be desired and I wonder how many different shocks the bike would accept. Overall, and based on admittedly limited experience, I'd go with the Giant.