H&S or Spartan. Keep your stock stuff. The only 6.4 engine problems we've seen are due to dusted engines from aftermarket air intakes. Also the crappy radiator end tanks go bad and leak on some of them. Everyone I know that had done a DPF delete is running H&S mini maxx or black maxx.

 

Good post 509. Keep an eye out for dusted low pressure turbos due to poorly installed filters and intakes. High pressure fuel pumps and corroded front covers are also an issue.