According to the SMG brochure, the standard range of Garmin Fish Finders are designed for freshwater use, ( maybe saltwater is thicker) so they have now brought out the "Blue" seies for saltwater use, with increased power and dual frequency. As the blue series are only a few pounds more I would go for one of those.
As for which model, they all have more or less the same functions, so it's really only a choice of size. Normally, biggest is best, just make sure you have room on your console!
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