It depends on the amount you are needing to spend or not to spend, but for the trolling motor I suggest the HDI transducer.
If you are trying to keep your cost low, look at the HOOK2 HDI models with Lowrance. The HDI models in 5, 7, 9 inch screens will provide Sonar, Downscan and GPS Mapping. If you want true mapping stay away from the models with 'x'. With the HOOK2 Lowrance unit 'X' means that it only has a GPS Plotter with no maps, but if you don't want true mapping up front the 'x' models can same additional money. If you can spend more go on up the Lowrance line to Elite Ti or Carbon models.