I think lava coral is currently the highest +2/2 on an armor .. only lava coral gives +2/2 if you are after mastery, all other pri stat mastery are +1/1 (tested ember topaz too) .. But there's a catch, on my lvl29's weapon, it's +3/3 .. So there is a difference between armor and weapon sockets.. I will test it for lvl10-19 later .. Not sure it will be the same.. Queen showed +6 str agil int, but becomes +3 on a weapon.. So a lava is better than queen