Because overindulgence of chocolate (an oxymoron for sure) is a legal vice, I suggest portions that are significant in size as well as height. If you espouse confectionary moderation, (another oxymoron), you may cut many more slices of dessert from a cake like the Chocolate Cranberry Conspiracy than the suggested 12 servings. The only downside to cutting more portions is that the slice of cake may not stand straight up but rather will need to be served on its side.
For professional-looking portions, use a 10- to 12-inch serrated slicer when cutting the cakes. Place the cake to be sliced on a sanitary cutting surface. Heat the blade of the slicer under hot running water and wipe the blade dry before making each slice.
When serving cake to guests, it's nice to take a few minutes to dress it up a bit. Especially at the holidays, a bit of garnish makes even ordinary cakes feel special. Depending on the cake, simple garnishes include sauce (raspberry goes well with chocolate, as does even more chocolate), fresh fruit, freshly whipped cream, chocolate shavings, small candies in complementary flavors or toasted nuts. Use your imagination!