The best approach in my opinion is pure stealth! Sure some missions force you to knockout guys. Although the obvious and easy choice is stealth. How much will you use? Will you sneak around and not get caught? Will you sneak around kill some, knockout some, and get caught? Will you just run around and slaughter any living thing? I personally prefer to not get caught, not kill, and not knockout(unless the mission says to do so). I have only gotten caught one so far but that was by The Golden Child and I had no Invisible potions and no way to get past him. I am curious to hear how you guys play.

I always prefer as stealthy as possible, using as few (hopefully none) of my supplies and no knockouts. Ghosting where I can.

Agreed. Play the game the way you want to play it. It's a nice feature of Thief that it doesn't force you to play one way.

I agree - one of the things I love about Thief is that you are generally free to make your own rules as you go along. I personally like to knock everyone in the level out, I find it quite therapeutic to whack them all on the head with a blackjack and then hide the bodies :)