To answer that question let's see what Jane Austen told us about Louisa's fall in Persuasion:
In the picture below we see the three movies with three versions of the different staircases.

Persuasion, the Fall – 1971, 1995 & 2007
When I read Persuasion for the first time I imagined a plain staircase and had no any idea of the shape of the Cobb. Finally, when I watched the 1995 and 2007 films I realized that the stairs were different, but certainly in the same place. The first, very rough, was made of steps embedded in the wall. The second wee finished in cement. I considered that the old staircase had been cemented at the time of filming in 2007, but then I realized that the steps were different and their positions were opposed.


Staircases - 1995 & 2007
Watching 1971's version, I saw the double staircase with woods in the background. I thought sincerely that they had filmed the scene in another place than the Cobb! I only believed that the locations were authentic when I discovered the Lyme Regis Pearl of Dorset's site and its webcam.

Staircases - 1971

Lyme Regis webcam screen shot
Now I changed the original question to: "From which of these three staircases did Louisa Musgrove fall?"
I believe I have found the answer in the book Jane Austen: Her Homes and Her Friends**, written by Constance Hill and illustrated by Ellen G. Hill (circa 1900), where the author describes her visit to Lyme Regis:
The steps in question are formed of rough blocks of stone which project like the teeth of a rakefrom the wall behind. We can ourselves bear witness to the “hardness of the pavement” below, which Captain Wentworth feared would cause “too great a jar” when he urged the young lady to desist from the fatal leap.

Staircases by Ellen G. Hill
* Alfred Tennyson (1809–1892), 1st Baron Tennyson, much better known as "Alfred, Lord Tennyson," English poet. Among his most admired works are Idylls of the King and The Lady of Shalot.
** Jane Austen – Her Home & Her Friends by Constance Hill, illustrated by Ellen G. Hill. Richard Clay & Sons, Ltd., London, 1901.
- Submitted by Raquel Sallaberry, Jane Austen em Português