What are the most difficult to find mods right now?

I currently think that Overeaters for one star and Rejuvenators for four star mods are the most desirable ones because they can be used by any player. Limit Breaking or Scanners might be valuable to VATS players but I’m not sure. Pounders will be useful until it is nerfed but players only need one of them rather than a full set of five for armor.