I really enjoyed this episode. This is a tough one because these are two of my favorite movies of all time and they are my two favorite PTA movies. They are the best representations of the two halves of his career. I'd argue that Boogie Nights made more of a cultural impact while TWBB tends to be talked about more in film fan circles so I could see an argument for that and I think more people would have a good time watching Boogie Nights.
I'm going with There Will Be Blood though not because it's the more "important" movie but because I think it's a better movie and I think by this point, Paul Thomas Anderson found his own style. I'd argue that while he wore his influences on his sleeves in the first half of his career, he made it his own but you still can't help but make comparisons to Scorsese and Altman. There Will Be Blood feels like it's truly his in a way Boogie Nights is not, at least on a filmmaking level. One thing that Devin and Amy didn't mention and I think most people overlook is how funny There Will Be Blood can be, at least once you are familiar with the movie. Every time I rewatch it, the funnier I find the dynamic between Daniel Plainview and Eli. Watching it in a theater a year and a half ago was interesting because of how often the audience was laughing in a movie that is seen to be so serious and important. Also a note about the ending, I don't think the music at the end is meant to show how important the movie is. It calls back to the scene where he first opens the oil well in Little Boston where that same piece is used.