Combat is good from the start, use a rupture talent build. Prioritize rupture on bigger elites/bosses, eviscerate on smaller trash. You don't have to worry about ArP when you're still gearing for up to 245 items. 251 items and above start prioritizing ArP as passive, don't gem ArP yet, keep using agility gems. Still, you shouldn't pass on good upgrades even if they don't have ArP. Work on your gear. When your passive ArP is closing in on 700, start gemming for Arp, as at this point ArP > agility gems.
At lower ilevels (before ArP becomes the key stat) haste means more weapon swings -> more 15 energy procs from offhand, and more poison hits. Crit means more combo point procs from SS, and you skills have higher chance to do more damage. At lower ilvl ArP won't benefit you as much as other stats.