My favorite is methylcellose. You can vary the consistancy and the color. And fairly easy cleanup.

2nd is shaving cream, just for ease of use for a variety of scenes and easy cleanup again.

My favorite substance, both to WAM with personally, and to watch someone else get covered in, has always been THICK, GLOOPY, oatmeal. It has to be thick, and warm; and mushy/sticky for nice coverage; the runny stuff is no fun. Other than oatmeal, I like cakes and pies, warm cake batter, cake frosting etc. and if we're going the savory route then some spaghetti probably. I pretty much like everything other than shaving cream/foam, but oatmeal is DEFINITELY my favorite

Mud's my faveourite, the stickier the better. Chocolate cake mix has to be a close second. Dislikes include shaving foam and anything green.

Wallowing in mud/clay is my best but methylcellulose is a great substitute indoors

My favorite is cheese sauce. The wife is away this weekend so its a trip to sam's club for a big can of cheese. It feels great and looks so wonderful.