One of the most reliable pumps you can put aboard is the FloJet (NOT ShurFlo). They were recently bought up by ITT, which immediately upped their price
-- of course.
However, for the moment these are still very reliable pumps. And, you can find them at discount prices. I've had a FloJet Booster Pump with 1.1 gal accumulator tank (built onto the same fibreglass platform) for the past six years and it's been very reliable.
However, FloJet has now come out with a variable speed pump which doesn't require an accumulator. It maintains a pressure of 30psi and 4.5 GPM flow, varying its speed according to need. It has a cutoff pressure of 40psi, so the initial delivery
of water is very fast and, when the pressure drops to 30psi the pump runs just fast enough to maintain that pressure level. Also, it uses a Hall-effect pressure sensor....no switch....which should be quite durable.
This pump, called the FloJet Sensor VSD, has had very good reports according to a marine
consultant friend. It comes in 2 sizes: 3.3 GPM and 4.5 GPM. You still may be able to find the larger pump for under $200.