BAC water is generally the go-to for most peptide reconstitution because of its bacteriostatic properties that slow bacterial growth (though it won't kill bacteria, so source quality still matters). BAC NaCl is another solid option and actually preferable for certain peptides/aminos, just worth researching first since some molecules don't play well with sodium chloride. The main time I see people going with plain sterile saline is with neurotoxins, though BAC NaCl makes more sense there if you're splitting doses and coming back to the vial later.