In general, you should keep the digital portion closest to the supply. A signal needs a return path to ground. The analog portion of your circuit is more adversly affected by noise. If your analog portion was closer to the supply the digital return current flow accross your analog portion when it returns.
Star grounding is a good technique but should be used carefully. In reality your grounding will vary from circuit to circuit. The goal is to minimize return path impedance, isolate sections based on noise level and susceptibility, and avoid large area for return path loops.