You must decide what kind of rider you are, the kind of rider you want to be and what your tolerance is for maintenance that you’ll perform or pay someone to do. Lets say for the sake of this discussion that they both have the same basic component spec.
- The Giant will be a better pedaling bike with its more nuanced (complex) suspension. Whether this is something you will readily notice will depend your experience and skill level. It is more of a trail/XC rig and is overall more mild-mannered of your choices. The big downside to the Giant is that it will be more maintenance intensive (more pivots) and will likely require return visits to your lbs to do so.
- The Heckler is a far stronger bike than the Giant. Bordering on bombproof. The most destructive rider I know who broke 3 Santa Cruz bikes (A Butcher and 2 Nomads) was finally warrantied a Heckler 7 and could not break it. It has a single pivot and is dumb simple to maintain. You could do this at home without much fuss. It may not pedal as well (more pedal kick back on square-edged hits), but it is the acme of single-pivot mountain bike design save the far more costly steeds from Orange. The Heckler is more trail/AM in design and will readily handle more rowdy rides.
My vote goes to the Heckler. It’s less costly, a great frame to build on, and a helluva lot of fun.