I am just coming back to the game and I was reading all the changes made to monster damage and so forth and I was wondering which would be better to use at this stage. I have 500-600 resist all and 32k HP at the moment.
It partly depends on what spec you use and what MP level you are running, but in general, the choice now is mostly Prismatic Armor or Pinpont barrier (or storm armor). Force armor is only really used by CM wizards tanking uber MP 10, or extremely low geared characters just getting into Inferno.
I use Pinpoint barrier as Archon, and try to use Storm Armor - Shocking Aspect as CM, but if I crank the MP too high I have to switch to pinpoint (the extra armor helps tons against electrified mobs and damage reflect).