From my understanding, HGH is superior to all IGF-1's for promoting new collagen growth, and many believe the combination of CJC-1295 and GHRP-2 or 6 is superior to taking HGH directly. The thought behind the superiority of the CJC-1295 and GHRP-2 or 6 combo instead of taking HGH directly, is that CJC-1295 and GHRP-2 or 6 work synergistically together to provide the body with multiple pulses of natural HGH per day. I've read that the CJC-1295 and GHRP-2 or 6 combo can produce up to 10IU's of natural HGH per day.
So to answer your question, HGH is best for collagen synthesis, and CJC-1295 and GHRP-2 or 6 taken together is the best peptide combo for natural HGH production. If money is a limiting factor, I personally would choose CJC-1295 over GHRP-2 or 6, but if you can spare the cash, take them both together. I've read that a dose of 100mcg of each taken via sub-q injection 3 times per day (morning, post-workout, and before bed) is a good starting point. As for which GHRP is best (2 or 6), they are pretty much interchangeable, but I've heard that 6 severely stimulates the appetite. Therefore, if you're looking to bulk up, go with GHRP-6, but if you're looking to stay lean, go with GHRP-2.
Just my two cents. Take it for what its worth, and good luck.