Like everyone says I think it depends on what you are going to make. I purchased a layer cake because the fabrics were very appealing to me but completely different from anything I had made before. So the layer cake gave me a sample selection of all of the different fabrics without my having to search. Also I had nothing in my stash that would "fit" with these fabrics. Just finished the quilt and I love it. But don't think I would do one like that again. Once is enough.
Also have to admit it did take me a while to find a pattern that used the layer cake.