I explained with details in an earlier post why I prefer SH over EF on Thok. Basically because P2 is really easy to heal. We had never problems with that. Our problem came in P1 when several ppl(say 4-5) goes under that critical health value where next screech will kill him. What you do with EF? This is the question I asked myself and changed to SH. Because HR isn't enough for all those if they are in different groups because range isn't enough. Ofc I can rely on other healers but I dont' want to do that if I can save those people myself with LoD even though it lowers my overall HPS a bit. Overall HPS comes from shaman/druid/monk, paladin might as well just concentrate on keeping those targets that are in danger of dying alive (LoD heals those critical targets and gives them illuminated healing which prevents them from dying on next screech).
Like I said, it is lower HPS overall, but killing a boss is not always about HPS. Think about this, 2nd time P1 and the only ress is used. You keep everyone topped with EF and huge HPS and then 1 healer makes a mistake with dispel and 1 target dies to screech after poison tick. That person just didn't happen to have EF on and died and it's a wipe. Of course it's nice to be on top of the meters but I personally choose killing the boss.
Of course this is only my opinion. Bash me if you want, but I had thought about this for a while and SH just feels better overall due to mechanics of the fight.
EDIT: My apologies, Pacer had already answered to this, which I did miss by replying instantly so I won't forget