It depends. For sleeves, I always do the increases or decreases slanting towards the seam. For something like a v-neck or armhole shaping, it depends what kind of look I'm going for. Decreases look more invisible if you slant them towards the edge/seam. For instance, look at the close up picture of the v-neck a ways down in this pattern
. The decreases are slanting towards the v-neck edge and they are not very noticeable. Now, take a look at the raglan decreases on this pattern
. The decreases are slanting away from the seam and they form a very noticeable ridge of decreases. Do you see what I mean after looking at those two pictures?? If you want
that noticeable ridge (which sometimes is a nice look, don't get me wrong) then go with the decreases slanting away from the edge, and if you want it more invisible, go with the decreases slanting towards the edge.