Victron, Sterling/ProMariner, Mastervolt are all well respected marine battery chargers.
Bear in mind, a multi bank charger only divides the total capacity of the charger across all the banks. In other words, if all three banks need charging, then the charger will provide 40a/3 amps or a bit more than 13 amps to each bank. Depending on how large the banks are, how they are configured, and the type of battery that may or may not be an adequate charging protocol.
This might be a good time to consider how you will use your boat and the battery needs and the kinds of charging your batteries in the future will need and take that into account as you consider different chargers. The ability to charge LiFePO4 batteries and to set custom charging profiles would be high on my list of desirable characteristics.