What like long torso is suited for one, short another etc. What one do you personally think is best wiggs? In general.
If you have a short torso, your waist in going to look more blocky. In this case, assuming you can, the vacuum style would be better. It elongates the torso and can make the waist look smaller.
If you have a long torso, do the opposite. BUT, flexing the abs too much makes the pose look ugly. It all depends on how you're structured. That's the jist of it though. There can be other things to take into account.