Thrown, "smushed", or simply "splatted" in there can all be good. I prefer it if it looks "natural" in the sense that if a normal person was going to smack someone with a pie, they just smash it in there and let it go. Messygirl pies never disappoint in this respect.
What I see in a lot of WAM videos is someone carefully placing the pie in an attempt to keep the crust intact, or maybe briskly shaking the pie from side to side to dislodge the shaving cream. It just looks decidedly unnatural.
Thrown, as in the Messygirl production "Mrs. Bee's Messy Humbling's" last pie hits (with side view) are awesome.
Pushed in faces, as in Dorothy Appleby in Stooge's "In the Sweet Pie and Pie"= also awesome.
I think the excitement factor is an out-of-the-blue pie thrown, but there's also something about the slow burn of a smushed pie that can be equally pleasing.
It's both, no doubt about it. Neither one nor the other is supreme. The ballistic drama of the exploding hurled projectile as it bursts over the face of its unsuspecting target is a beautiful thing, but it does not outmatch the controlled humiliation and gloating relish dealt by the deliberate push, twist and smoosh of the placed pastry.
Have to be pushed. With thrown it may or may not hit the mark and you can't really control where it goes. With a pushed pie, you can slide the contents up or down and determine where to push the contents. A thrown pie you can see it coming and prepare for the shock. A pushed pie, you can surprise the person.