When I was in baking, I always used frozen cake to decorate. It holds up better while you are working with it, especially if you actually sculpt the cake for certain things like I did.
Once the cakes come out of the oven, I let them cool till I can touch them with my bare hands, and then flip them upside down onto a cookie sheet covered with plastic wrap. Then I cover the cake layers with plastic wrap before putting them in the freezer.
While the moisture is still escaping from the warm cake, it will freeze making a thin outside layer of ice on the cake.
When unwrapping the cake layers for assembly, the frozen bits act as its own simple syrup, as when the ice melts it absorbs back into the cake keeping it super moist.
I have used simple syrups before, but usually to add flavoring to a cake or if someone orders "extra moist" cake.
I did use it as a standard on wedding cakes though, because the batter I used for wedding cakes was dense and thick, almost like a pound cake. Which is what you want when making a cake that is large or that will be stacked in some way.
As for your question, which is more difficult, it depends on who you ask. For me, I would say baking is the easy part............decorating, sculpting, or frosting is more difficult because its the finish on the cake, which you want to look as good as possible.