Had a Attwood S500 bilge pump and it quit. No idea how old it is, but the motor will not turn. Looking at the Rule and Atwood bilge pumps and was wondering what is the most reliable brand since (like most bilge pumps) it is a pain in the a$$ to get at. The boat is a 20' Formula I/O

It makes the job easier if you can replace it with the same model. The bottom half of the pump is probably screwed down in the bilge. You can just put the new pump on the old bottom.

IMO no one brand can be considered better then others. It is a rarely used electric thing that lives in the bottom of the boat so the reliability is always less then ideal. Every boat I have ever owned I add a second one wired separately to second battery.

I looked into doing this as well (all of our bilge pumps are a PITA) but decided against it because the newer models are generally more electrically efficient and use less amps therefore; could run longer if they had to before the battery died.