One of the most authentic reality tv shows, while not on today would have been The Real World. But honestly today, just in general there is way less authentic or natural shows. Its all about ratings, so these producers are now required to prod and poke people to create narratives and situations. They want interesting TV. This also then goes back into the editing of shows. They're going to put out what they think will garner the most views. Reality TV was a lot more natural 20 years ago. But as it has become more popular, and social media which i personally believe is the greatest harm to reality tv, the industry has shifted.
The Bachelor used to actually cast a real Bachelor with a career, and was set up in their life in their 30s. Average age of contestants were probably late 20s, early 30s. But if you look at the franchise now, it is just filled with Instagram influencers that wants to gain followers. They practically only cast people under the age of 25, and a majority like under the age of 23. Its obvious these people are mostly here to try and gain fame, rather than actually get married. The people they cast are no where near ready for marriage like how they use to.
I've watched reality tv nearly my entire life and it sucks to see the direction it has taken. However, regarding the major reality tv programs that have been on for a decade+, I think Survivor has done its best staying close to its roots.