They probably have the greatest market share -- maybe Jabsco is up there.

Johnson, in the size range you listed is supposedly the quietest that PS reported. Noise is good if you have a leak and want to be awakened in the middle of the night instead of draining your battery and your tank ;^)))

Defender's prices knock the socks off of West Marine's prices. West has its "brand", may be made by Jabsco?

I have been happy with SurFlo.

I WONDER IF YOU HAVE A LEAK, if you don't have an accumulator tank and a Surflo pump?

One way to check: i) turn-on the pump, ii) after a good while (when you're sure you've pressured the system), turn-off the pump, iii) don't open ANY fixtures, and iv) after about 5 hours or so, turn-on a valve. If you don't get the sign of still having pressure from the flow, then you may have a leak somewhere.