Like everything-it depends
Do you want to de-water a boat that's been holed? Or just dump the bilge water from the packing gland and minor spills? Some use two pumps, one a BIG one to dewater in an emergency which is set up on a small platform in the bilge, and a smaller second one, set in the lowest part of the bilge, to drain the packing gland piddle. The platform the big one is on is set high enough to stop it from doing the frequent on/off thing (and the consequent heavy load on the battery), while the small one (which uses less juice) cycles more frequently. Personally, on my outboard powered 27, I have a 2500GPH Rule. But then, with OB power, I don't worry about packing glands. I just want to keep ahead of the water long enough to rig up the collision mat if I hit something.
