I ranked each cast on placement and on the average amount of confessionals each contestant received per episode, that way I got one list to represent presence and another to represent longevity. I then took each castaway's average rating across both lists, punched all the ratings into a normal distribution chart, and based on who is in the top tier, that gave me the "main characters" of each season. I included their average ranking across both lists.
Borneo: Richard Hatch (1/16) & Kelly Wiglesworth (2/16)
The Australian Outback: Colby Donaldson (1.5/16), Tina Wesson (3/16), & Keith Famie (3.25/16)
Africa: Ethan Zohn (1.75/16), Lex van den Berghe (2/16), & Tom Buchanan (4/16)
Marquesas: Kathy Vavrick-O'Brien (2.5/16) & Sean Rector (5/16)
Thailand: Clay Jordan (3/16), Helen Glover (3/16), & Brian Heidik (4/16)
The Amazon: Jenna Morasca (2/16), Rob Cesternino (2/16), & Matthew von Ertfelda (4.5/16)