CR-1 or K1

Hi fellas,

Partner (US Citizen) & I are in a 3rd country outside of the US. We plan to move to the US ideally next summer; if not, by next winter. Which would make more sense for us, CR-1 or K1?

Also, as I was previously on a OPT when I did my Bachelor's in the States, I already have a SSN card. Would I need to reapply for one?