**It makes absolutely no difference.** To illustrate why, let's break down the individual changes in direction by 90° segments through the trap, beginning with the vertical drop out the tailpiece:

1. To horizontal
1. To vertical (upward)
1. To horizontal
1. Through any horizontal bends to the tee

_None of this changes_ when you swing the trap pivots. It's always exactly the same sequence. While a fluid dynamics geek could argue the finer points of the forces involved, the variation is negligible for purposes of an unpressurized drain.