I use Bacteriostatic water as I find it is the most comfortable to inject. I found other sterile waters sting while injecting them but with Bac water there is no pain at all. I also read somewhere that it stays fresh longer aswell. I stand to be corrected on this if I am wrong can't remember the source I read it from.
Sodium chloride is for immediate use peptides (ie.: TB-500), with melanotan peptides you'll prefer the product with a bacteriostatic agent (as BoB.org says). Bacteriostatic water and bacteriostatic sodium chloride are both great for mt2/mt1.