Basically due to spellpower difference you are best taking the first thunderforged caster weapon you can get and building around that. As has been mentioned the staves are "easier" in that they only require one lucky roll (winning the loot is another matter lol). Also you can't get an OH without crit which is not showing consistently as our weakest stat over all 3x specs. So in terms of collection of stats the staves are better this tier. Though not so much better you aren't better off using a thunderforged weapon and just reforging the crit vs a perfectly itemized conventional version.