It depends.
Are you going to be going on long voyages, without the easy availability of shore power and fuel? If so, no, a generator doesn't really make sense. Wind and solar power would make far more sense in that case. Generators are probably as heavy, if not a bit heavier than solar panels or wind generators, and require you to carry enough
fuel to run them for the duration of the passage, while the solar panels and wind generator do not.
If you're just going on short, marina-to-marina coastal trips, then a generator might make sense. Generators can be fairly noisy and produce noxious fumes, and if you are going to equip one on your boat, make sure you have a good CO detector, preferably one that is wired into the generator, to kill it if the CO levels rise.
Which generator to get? It depends on your boat. I would get one that uses the same
fuel as the boat's main engine. If your boat has a diesel in-board, then get a diesel-powered generator. Likewise, if your boat uses a gasoline powered outboard or in-board, get a gasoline powered generator. Honda, Panda, Kohler, Westerbreke, and Fischer are among the better known and regarded generator manufacturers. However, not all of them make a smaller, portable unit, which is probably what you will ned on your boat, as I doubt you have the room for a larger, permanent installation.