Croqueteer, the advantage that the Nimrod had over the Shack, and by extension the Atl, was a high transit speed enabling it to reach a patrol area 1,000 miles out in about 2.5 hours compared to double that in a Shack. Faster transits enabled fewer airframe to maintain a patrol box.
On patrol the Atl speed would be around 190 kts compared with around 225 for the Nimrod. This enabled either a faster revisit time or a larger patrol area for the same revisit time.
However our boss at the time opined that the floor level on the P3, and by extension the Atl, was better as it was lower allowing more room for the crew at waist level (no cracks about the galley) for moving about.