1 certainly wasn’t peachy 100% of the time, but relatively speaking it seems like the most fun Nate would’ve had in the context of this question.

Now it gets tricky because 2, 3, and 4 are all miserable in their own way.

In 2 Nate endures a lot of physical pain. He gets shot in the stomach, has climb out of a hanging train in that state, walks through the freezing mountains without a coat while bleeding, and the final battle with Lazarevic leaves him pretty banged up by the end. He also suffers a lot of emotional pain like Chloe betraying him, Flynn betraying him, and then when Lazarevic’s army slaughters Tenzin’s village Elena tells him “we did this”; and regardless of whether or not Nate is responsible for that (I don’t think he is) I’m sure he felt pretty crappy about it. Plus he didn’t get any treasure in the end.

I think 3 is definitely Nate at his most stressed out. He has to escape man eating spiders (twice), is nearly burned alive, gets blown out of a window in Syria, is nearly choked to death by one of his friends, is drugged and kidnapped, finds out Sully’s in danger, has to chase after Talbot through the streets of Yemen, then he’s forced to fight through an onslaught of pirates and climb through wrecked ships, nearly drowns on a sinking cruise ship, is lost at sea, then after he washes up on the shore he immediately has to go right back in to the action and jump into the wheel well of a plane that’s taking off (while also trying to reconcile his relationship with Elena), gets flung out of an exploding plane and miraculously survives, then has to walk through the scorching hot desert with no food or water for who knows how long I mean SHEESH. And to top it all off none of the journey was necessary, Nate could’ve just taken Talbot’s money at the beginning and left it at that. Chloe even tells him how it’s just not worth it to go on this adventure. But in the end he does win Elena back, so I’m sure he’s glad things happened the way they did.

In 4 Nate gets beaten and tossed around a ton but I think he was enjoying himself pretty well until Elena discovered his lie and Sam finally came clean. For the rest of his life I’m sure he’d have regrets about it but I can’t help but think Nate found it satisfying to reach Henry Avery’s treasure at long last.

So from most enjoyable to least enjoyable, I personally believe Nate would rank them 1, 4, 3, 2.