old-school player, asking a noob question...

[Legacy_MagicalMaster]

               Mind Spell Immunity is better.  Otherwise most characters run away like an idiot if they get feared and get Paralyzed by Bigby's.  Plus other stuff.  Death is likely the second best immunity in many cases, depends if enemies are actually using Death Magic with high DCs.  THEN you might find Critical Immunity to be the best, but even then Level/Ability Drain Immunity can often be better.
               
               

               
            

[Legacy_Drewskie]

               mind and death attacks are both situational.  basically any hit roll in the game at any time can potentially crit... and there's no immunity spell for it either.
               
               

               
            

[Legacy_MagicalMaster]

               Except even a weapon master is only going to do 80% more damage to you in the best situation (100% for a Scythe).  So, with the exception of Dev Crit, the worst that happens from lacking crit immunity versus a build incredibly focused on crits is you take double damage.

Plus AC and concealment already drastically reduce critical strikes taken.

Now, true, there's not a spell for crit immunity -- but that wasn't a consideration mentioned '>  Simply which immunity was the most important.

A dragon, for example, will do <10% more damage to you if it can crit you AND has Improved Critical.  Not exactly game changing.