Personally, I think I would go with the free healz. Raids and such where your primary focus is healing, free clw + heal scrolls can save you a lot of sp, and (despite what some zergers may think) staying alive is more important that killing everything quickly (but if you can do both thats a plus

). Plus, its free healing! You cant go wrong with that.
Searing light sla seems decent, but isnt as appealing to me as clw sla. It saves you some sp but.. soloing, you wanna group stuff up and aoe it, in a group you want to ether melee, group stuff up and aoe it it, or heal. Might be worth testing to see how much damage it does at endgame on trash when you solo.. but not sure it would be for me.
Long fights: Nether is essential, but healing sla saves you sp if you are healing the tank in a place where you cant aoe heal everyone with him (horoth fight for example) and saves your sp so your prepared for the o**** moments. If its not a fight where you need to be healer full time, or dont have to worry too much about sp (shroud), searing light could be better.
Long runs: In groups, healing. Solo, toss up, maybe favoring searing light, depends partly on the quest (how much can you zerg and aoe?) and what your melee capabilities are (more melee => free healing better as you already have free damage).
Hard fights: Tempted to say neither, because in hard fights you will be using stuff other than your sla's. May go with what I said for long fights, healing sla saves sp for the important stuff.
I would say its partly opinion and playstyle. I (dont own fvs but think that I would) prefer clw sla on my fvs for saving sp healing tod and other raids like that, and for group maintenance in harder elite quests.