My personal way to play Omniknight is to usually get a level in Repel at level 2. In fact, if you are laning against silencer, you really should get it level 1. He casts curse, repel your ally. It is also great for disarming ganks from mid. If I get stuck in a Solo Top/Bottom, I will skip Degen for a while, and simply dump points into stats.
Some situational items I like picking up on him is an Orb of Venom, and a Heaven's Halberd.
wadafuq. Idk how many times i've nearly gouged my eyes out at seeing omni NOT get repel at level 1. There are so little instances where a 80 heal/60 dmg in a small aoe spell has been more important then absolute spell-immunity for 6 seconds (because at level 1 no one has an active spell that goes through repel par troll warlord). Omniknight is played in a defensive manner, and as such repel is one of the best anti-ganking spells (among other level 1 cockblocks like fissure) and by no means should be ignored for "omg level 1 purification its a heal". So unless you can mathcraft me a reason why you would go purification at level 1 over repel, don't give bad advice please.