***HEELP STR OR ARP?!?!***
That depends on your gearlevel, do you have a Grim toll, Molnir runestone or Needle-Encrusted Scorpion? If you do, it would be your best interest to gem for arp until you reach the soft cap(read above).
No Molnir runestone, grim toll or Needle-Encrusted Scorpion? Can you reach more then ~75% passive arp(*This is a rough estimate and depends a lot on your current gear! Consult your spreadsheet to be certain*) without dropping your hit and expertise far below caps? If you can, then you should.
Dont have a either GT, MJ or NES(Lulz, funny abbreviation) and can't get that high passive ArP? Stack strength.
OBS: These are rough way lines, for the most precise answer, head over to Elitist jerks -> warrior forum -> Landsoul's spreadsheet.