Hi compet_pl, just get quick pet hate out the way; you can't have "most silent!" Lots of people make the same mistake, many of them whose first language is English... Silent is an absolute term, something is silent or it is not, there are no degrees of silence. Same with unique, it's unique or it's not, you can't have most unique or very unique, that's like saying something's the most dead!
Anyway now I feel better [and not really your fault, I see this kind of mistake too much, even from professional writers that really should know better...] and will try to help
I have no experience of these card but presume you have to have it low profile, and you want as much performance as possible.
Looking at them I would not go with the Sapphire card, the cooler is smaller and will have to work harder, i.e. louder, to get the same cooling. Furthermore with the HIS card I can see fan swap being possible in a way that it wouldn't be with the Sapphire card.
I would suggest get the HIS card and see how it is. Often they run the fans much faster than really needed and you can use software, like MSI Afterburner, to alter the fan speed curve. That is trade less noise for higher temperatures, especially at idle. You may also need to "mod" the cards BIOS to reduce the fan speed, or just fit different fans.
Good luck, Seb