Color is a bigger deal than you might think. I was skeptical at first that it amounted to anything, but it is certainly worthwhile. Your basic choices are a conventional 2D sonar, a down-imaging sonar or an HDS/LSS system that has both 2D, DI and structure scan.

Lowrance has the Elite and Mark series with conventional or DI, in mono or color to look at Fishfinder, GPS Chartplotter | LOWRANCE Mark or the HDS series for the structure scan.