Indeed, there are far better items you could be getting rather than lifesteal. You can either focus on damage or survivability. Personally I'm getting the much maligned vanguard as an item which gives good hp regen, a nice health boost and some damage block for when you're tanking the creep waves to regen health, and then moving onto a shadow blade to help with the ganking, then actually going for a skadi since I get the orb of venom early on, it gives decent stats (Ulti orbs help with everything) and the orb works in duel, so it means you're safer using it on their carries.
After that, go for damage; desolator followed by daedalus, the desolator does work during a duel I believe, while you won't get the crit from daedalus.
Of course you can go for a pure damage build by skipping those, but I prefer the survivability from vanguard/skadi, getting easy dual wins to build up the attack damage. Plus as you win more you're going to become a bigger target, so the hp from those items is a lifesaver.
