It all depends on the purpose for which you are doing the quilt. If it is one for camping in the cold...lots more thickness than if it is to be used in my nice warm home. And if it is for judging, possibly even different criteria.
I personally like doing just the top and fleece. Quick, easy, inexpensive (I got several bolts of fleece at $3/yd on sale 3 or 4 years ago), and most important of all, very snuggly! Plus most of what I make is throws, so no need to piece the fleece.