Wallas is quieter than some others and easy to service. Designed from the beginning for marine use - the others are not.
I can't say from experience or technical knowledge which is quieter. Our Espar makes some noise, and there are two main components to it: The fan and the fuel pump. The combustion chamber and fan sound like a little jet engine, but you have to strain to hear it. The fuel pump is a deep tick-tick. It is noticeable when the system is on low and I'm working on quieting it down a bit. It doesn't bother me at all, but does irritate my de-facto spouse sometimes. That said, all the systems will have a fuel pump of this nature. There is flow noise through the ducting and out of the registers, but I'd imagine this to be pretty close across all the brands, for the same duct size and CFM.
As far as the design goes, the design parameter that I've noticed is that the Espar, as mitiempo notes, was originally designed for buses and trucks that have an alternator running, so they like 14.1V. I don't know about the others.
That said, if it was originally designed or redesigned isn't really as important as if however it was designed takes into account the marine environment, intended service, and customer needs. I've seen plenty of originally designed for the marine environment equipment that was most suited as artificial reef material.