Crit chance. But you also didn't say for what kinda of playstlye. Single out is really only used these days for solo or 2-man groups and 95% of the time only for the Rift Guardian. Because with sader in the group, they give a 20% Crit hit chance buff.
Crit chance is very important for Nats, because you are relying on Crashing rain. You want that to crit as much as possible. You want your crit chance to be at minimum 50%. With Nats your Crit hit damage will always be decently high, because of Duel wield.
cdr, chc, socket, dex on both rings (assuming you gain chd from dual wielding) is the ideal priority for N6 builds.
If your rings are not ancient or low on dexterity, then you have an option to roll dex to smt else; in my case I would pick attack speed because I'm not using the stereotype strafe N6 build and AS is almost as good as cdr for me..
If you re dual wielding you probably want CHC over CHD. You will buff CHD with a 2nd weapon gem but you lose the quiver slot that can roll 10%CHC. Which is another reason to use the passive Archery, you get a lot of value from a 5% CHC boost with the higher CHD from dual wielding.