Seasons 1 +2 is a good start for Survivor. The two winners pretty much show the two main ways to win the game, and the two play styles of Survivor. Pretty crucial seasons. Other seasons that I think are important watches, either for quality reasons or because they say something about the game itself:
Marquesas
Amazon (Maybe. I've seen it described as a parody of Survivor almost, so not sure how good it would be without seeing all that came before.)
Pearl Islands
All-Stars
Vanuatu or Guatemala
Palau
Exile Island
Cook Islands or Fiji (Bad seasons, but are reflective of the way the game has changed)
Micronesia
Samoa + Heroes Vs. Villans (Bad editing, but at least tell an interesting story about playing Survivor.
Season 2 for Big Brother. The first "proper" season, and still the best
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My bracket wasn't good enough to beat SuperNiceDog's in the GameFAQS Rivalry Rumble. Congrats!
This is Yesmar.