It's difficult to generalize since the "best" position for the steam wand depends on the steam's dispersion pattern and its velocity/volume. However, if I walked up to a powerful steamer with 3 holes or more, I would first try dead center and straight down. Otherwise my preferred technique is described in threads like
Still can't froth milk properly and excerpted below:
HB wrote:Assuming you have enough steam velocity, do an end-over-end, otherwise a vertical spin as described in
New Andreja owner with microfoam problem. If you're having trouble with texturing, try creating a vortex like this:
Sorry about the quality of this diagram...The pitcher is tilted to the left and towards you; the force of the steam wand is directed downwards and slightly towards the front and right. You should be able to get a nice "offset" vertical spin with a 20 ounce pitcher and 9 ounces of milk. With a 12 ounce pitcher, you must pay attention to avoid splattering. When done correctly, you will see the effects of the liquid rebounding off the bottom of the pitcher on the opposite side. It is not an end-over-end roil; Anita doesn't quite have enough steam for that.
That said, be wary of microanalyzing minor issues like steam wand position. More important is recognizing the
sound of the zone between air injection (think ripping paper, bacon frying), soap bubble introduction (blowing bubbles through a straw), and texturing (low rumble). You may find it helpful to
practice steaming with soapy water as advocated by Scott Rao.