In the class system of WoW,Priest,Mage,Warlock,Elemental/Restoration Shaman,Restoration/Balance Druid and holy Paladin,shaman and pal can hold shield that not necessary to choose,So the problem was for the remaining,staff or main+off.
　　As a frost mage,haste staff or a off hand of Resistance lower could be better,here's the comparison：

It seems staff got advantage,92 haste are more attractive when compared with 39 critical,so does enchanting,only 78sp lower.

　　However,don't ignore the Resistance lower,I don't know what you treat the Resistance lower like,but It's requisite,and my level was 120.

　　Then the socket of s6 suit,1 blue in glove,trouser and weapon,and the bonus was all spell power that not able to be given up,so the gem of combined stat was better,enchanting 35Resistance lower in back(*35Resistance lower was more valuable than23 haste),then the staff,Resistance can reach 95 when gem 20Resistance lower for 3 blue sockets ,S6 Wands provides 31 Resistance lower to get 126,or change one gem into 9sp 10Resistance lower,then the Resistance lower was 116 and 9 more spell power.

　　The main+off got 55 more Resistance lower,3gems can be 9sp12sta or 8 haste12sta,wen calculated with gem of sp+sta,it got55+31+35=121Resistance lower,perfect.And it got 27 more sp and 36 sta.

　　Means if choose 8haste 12sta,the main+off got 2Sta 3int 10resil 76Haste对39Sta39crit5Resistance lower；and the difference was 57Sta 39crit 5Resistance lower when using  gem of 9Sta12Sta　

　　The only thing we could change was the weapon after the battle start,so we'd better not put some gears of Resistance lower on these "steady space",or it may useless for those team without mage or druid.

　　I got detailed comparison above,and wish more opinion and advices.