[erisia]

I've tested both and found Lum Berry to be more useful in general. It lets Exeggutor switch into status attacks from faster users without taking the residual damage from Burns or Toxic (it highly reduces the chances of Misdreavus OHKOing with Will-O-Wisp + Shadow Ball after Eggy's taken some residual damage, for instance) Plus it avoid unfortunate circumstances where Exeggutor switches into a Thunder Wave and gets fully paralysed at eggsactly the wrong moment. Chesto Berry will get an AC mention for sure, though.