Of only those two... neither. QD is ok if you plan to install/uninstall often. However, Mash hooks are far superior to both IMHO. Mash hooks were designed to address all the shortcomings of HK hooks and do so marvelously. I have no idea why Mash hooks have not caught on more (other than most people don't even know what they are) as they ARE superior in EVERY aspect.
That being said... HK hooks are junk and I'd avoid then at all costs. QD is fine (as said above, get RL versions), but not necessary unless you constantly sling/unsling your rifle. Mash hooks are simple, no moving parts, strong, and will outlive you.
Even with all of that... I prefer NO attachments. As in... sling it right to the sling swivel or slot in the stock (as in no disconnect). 1 less part = 1 less part to fail. JMHO.