Vitality gives the most return, strength second and dex isn't even close to being worth putting any points into. Strength is barely worth the points since it takes a large amount to hit the next percentage of mitigation. The 30 points in strength will not increase your dps any noticeable amount and same with threat. We have more than enough threat generation, especially once we get Shield Oath. There were several detailed charts that broke down all this in the phase 3 beta forums. Vitality gives 450 more hp, more hp regen, more stoneskin bonus etc. I for one think the bonus stats are silly to begin with, but that's another topic