Life Steal becomes useful after you hit 60 to 70k dps on your character sheet. Before that it is minimal and a few hundred LoH is better. At higher dps it does start to add up and combined with LoH can be pretty useful and is much cheaper than LoH on weapno.
The game is about balance, I've dropped some res for life leach and it has helped me a lot. I got 600 LoH atm and it's really good, but with 700+ res I'm still on a good amount of Resistance so I can leach health and don't loose that much in the procces.
Remember to balance, you CAN drop some resistance to get LoH but don't go insane. Best solution is getting a nice weapon with lots of LoH or a socket and a nice gem on it.