I had the singular good fortune to fly the Shack, Neptune, Nimrod and Orion, with at least 1,000 hours on each. I loved them all; great aircraft and crews to go into battle with!
I think that the low altitude noise signature is irrelevant. In modern ASW the MPA will spend the Search/Detect phase at high, fuel-efficient altitudes. The submarine can only detect the MPA noise signature if he is shallow and the MPA is at low level.
So it boils down to jet versus turbo-prop.
My strongly held belief is that any MPA
must have four engines. My experience would ask for a new design of airframe, with a flexible wing to ride the bumps; a weapons bay as big as the Nimrod; four new-generation turbo-props, which have 'loadsa' thrust and efficient curved blades, plus in-flight refuelling.
Perhaps a design incorporating the best of the Nimrod, Orion and, yes, not forgetting the Bear Delta. That would give us a full Pint, replenishable too!
