What energy sources do you have available? What size is the electrical supply (main breaker or fuse)? How cold is the incoming water from the well? Do you have natural gas available or willing to put in a propane tank? An electrical tankless will be limited in volume unless you have significant electrical power capacity - the smallest one might overload your power panel. A tank-type electrical WH is probably the easiest to install and probably wouldn't tax the incoming power. I'd turn it off and drain it for the winter. You must ensure it is full of water prior to turning the power to it, or you will quickly fry the heating element(s).