The Heal is nice and happens more often than you think it would, in PvE anyway. While extra damage is nice, staying alive to deal the damage is even nicer.
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"
Flame lash for PvP lava whip for PvE. Flame lash healing also works on PvE but not on bosses for example. and You can heal Yourself on PvE with burning embers a lot.
I would never run lash in PVE. You already have great heals in burning embers and deep breath, plus healing is your healers job. Molten Whip is your main spam skill so lowering the damage on that is a really bad move.
In PVP, Lash is better. It procs a lot, especially if you are running burning embers.
If you play both evenly and dont want to swap, I would run Whip.