A24 volt will give you more Power, makes a big difference when trolling in the wind. It is heavier and more expensive. The 12 volt less weight but not as much power. But you can get 2 batteries and troll twice as long. Plus you can use your boat motor battery with it if you want. If you troll when windy or in river currents go for the 24 volt. If on calm lakes mostly consider the 12 volt. Although expensive get a model with autopilot. Worth every penny. On a breezy day without auto pilot you will be correcting your direction constantly. With autopilot set the direction and forget it. The autopilot will keep you on course and make all steering corrections.
What type of fishing do you do and where? Big water, small water, rivers, coastal areas with tides and currents??
Hunting, fishing, Labrador Retrievers and at the end of the day a glass of Forty Creek Barrel Select Canadian Whisky - Life is sweet