Good advice here...I've used both Kona and Bella, but haven't had access to Marshall', and have no preference one over the other. At my LQS, solids are priced lower than other fabrics. Like IceBlossom says all blacks are not the same. If you stick with one brand you will be just fine.
I'm finding I'm using more solids than before, but like to use pieces that read solid to give some depth to the patchwork.