At the point of contact, the racket face should be pointing almost exactly straight out into the court. This is true regardless of the type of serve. Depending on the degree of spin and pace, it varies a bit, but not as much as you might think. Take a look at slow-mo videos of pro serves.
If you are hitting topspin slice, you need to hit the ball up a bit more because the topspin component will pull the ball back down faster than just gravity. The opposite is true for underspin I suppose, although you don't see too many underspin serves (too hard to get over the net I guess).
Do not confuse the angle of the racket at contact with the direction of the swing. In a slice, the racket will be moving left to right across the ball to create side spin. Other serves require different swings to create the different spins.