My vote is also for the Rule 500, but the electronic version. Had one on my last Whaler for 8 years and it worked great with no problems.
I installed the same pump on my 15 Whaler and expect the same longevity out of it.


on edit - the electronic version turns on every several mins for a split second and if it does not sense resistance, it turns right off. If there was water, it would stay on and pump until dry and then shut off and go back to it's schedule of every few mins. Some people do not like this feature and worry it will drain the battery, but I've left the boat for weeks at a time and it's never been a problem. This feature is in place of of a separate float switch and I'm not a big fan of Rule float switches in a small boat that bounces around. My experience is they have a higher rate of failure.
D-