Whats the best memory for me?

im building my 1st computer and i was wondering what is the better memory option is Corsair Dominator 24GB 1600 MHz CAS 9 DHX Triple Channel Desktop or Corsair Dominator GT 12GB DDR3 1866 MhzCAS 9 DHX XMP Fan Triple Channel Desktop my motherboard is an asus sabertooth x58 and prosseser is an intel i7 960 3.20 ghz they can both take up to 24gb of memory it says