from what i understand LOH isnt allways 100%, it depends on the skill, like if you have 1000 lo, when you use FOT with thunderclap you only get about 750 life per hit.
as well, Loh works as a per mob.
so like say your FOT with TC aoe hits a mob, then you get 1 hit for the original monster you hit and 1 hit for the mob behind it so then assuming you had 1000 loh youd get 1500 life.
as well LOH only works with some spell'a mainly the spirit regenerators, sweeping wind and backlash dont work with it.
compare this to Life steal, its allways what ever the % is - % reduction due to difficulty. so if you have 3% life steal and you use FOT for 100k dmg in inferno, you get 600 life. same if you use crip wave, do 100k dmg, you get 600 life.
now all aoe attacks work per mob, but with life steal the damage is combined. so lets say you have a mob of 8 monsters and you use crip wave dealing 30k dmg to each monster, this means that you really did 240k dmg so you would get 1440 life back (in inferno).
as well from what i understand i belive that Life steal works with all Dmg, so for example life steal works with sweeping winds, and backlash.
personally i feel that a combination of LOH, Regen, and Life steal, is best, aswell for a monk life per spirit spent can play an important part but not as important.