You usually get what you pay for. In general, the better a marine stereo’s specifications the better the resulting sound. Receivers should have a wide frequency response, lots of RMS power, and if you still like to listen to FM radio, a low FM sensitivity specification. Still listen to CDs? Look for a high signal-to-noise ratio. Don’t scrimp on speakers. They should have waterproof, not paper, cones, rubber surrounds and grilles that stand up to constant exposure to sun and the elements.