I like turning mine both inward. I don’t know why, but I find it annoying when both are turned outward, or both are turned facing the same way. Facing straight ahead or backward removes the shape from the silouette. And random facing is probably the most annoying of all.
Like good soldiers, they must always face the enemy. In fact, before I move them I always face them towards their target so that the bastards see the face of their capturer.
I usually face mine to the right, or right front. But then again I don’t play very much board chess, most of mine is done over the computer. At least now we know how to rile Lib if we ever play him. 
I set mine up so that they point at the far rook squares of my opponent, and keep them there if I remember.
Removing the shape from the silhouette may work to your advantage. By stealthing your knights, your opponent has a lesser chance of anticipating a devastating knight attack, or of falling prey to a trap involving knights. Thus, I always point the heads forward - in those cases where your opponent is not so daft as to not realize they are there, this stance is most intimidating, so you get the advantage either way.
Forwards.
I hate the sneaky bastards.
I’ll trade a bishop for one any day.
I very carefully balance the knights on their heads, facing away from me, in order to weird my opponet out.
Inward, facing the enemy. Any other orientation bothers me a bit.
(Note to self: Never get in a game with RandomLetters.)
You should try to get over that (I suggest playing through some master games where the only advantage is having the bishop-pair).
I face mine sideways, but harbor no preference for both left, both right, both in, or both out.
Forward. Otherwise, how could the little horsies see where they’re going?
Forward.
But I could see turning the horse to the side if that would make the knight himself face forward
I generally face them in the direction they last moved.
How do you determine if he moved over one and up two, or up two and over one?
I don’t think horses can see straight ahead, with their eyes looking to the side
Yeah, you know, that’s why at horse races all the horses run SIDEWAYS.
Forward. And it drives me nuts when people do otherwise. It’s like not having your piece in the center of it’s square or something.
That’s a way I’ve never seen or heard of before. How did that come about?
Forward.
But it doesn’t really matter how I do it–they are both soon taken by my son…<sigh>
They face my opposition, just slightly tilted to the middle of the board so I can grab them with two fingers on either side of their face and the thumb at the back of their head without twisting my wrist. If a knight on the left side of the board, I use my left and vice versa.
Because I always trace out the path with my piece.