Here is something i posted for someone else asking about LEECH vs LOH.
Life Steal is nerfed by 80% effectiveness in Inferno, meaning only 20% of a 3% weapon will work. which is 0.6% total life leech.
Lets assume you hit normally for 20k (non-crit), you just leeched 120 life. wowbad.
To reach even the lower level weapon LOH of, say, 300... you would need to hit around 60k non-crit or stack around 9% Life Leech (1.8% LL in Inferno).
Comparing to most endgame LOH stacks of 1000, you would need to do hit around 200k dmg non-crit or stack over 13.3% Life Leech (7.98% LL in Inferno).
TL;DR? Life Leech is TERRIBLE in Inferno, but works very well in all other difficulties. LoH is a much better choice in Inferno since it is a flat value.
(affected by RATIO chances per ability::
http://www.diablowiki.net/On_Hit_Modifiers &
http://us.battle.net/d3/en/forum/topic/5149154265)