Weinberg, The Quantum Theory of Fields, Vol I.
One of my favorite Zee quotes (from his ASTI lectures, I believe) is that, “The only person who can understand Weinberg is Weinberg.” The three volume set is a treasure trove of insight into QFT by one of the greats. Unfortunately, it’s nearly unreadable for someone who hasn’t studied QFT before. Even the typesetting, with its super-curly letters, is opaque. What I like about it: This is QFT taught by someone who’s spent a lot of time thinking about it (and contributing significantly to its development!). It’s full of lots of really deep insights. Why I was confused: … but for someone with no prior QFT background, extracting knowledge from Weinberg is like pulling teeth. His first volume approaches the subject from a different direction than any other text, making sure to take time to point out several subtleties along the way. A proper reading requires respectable background of representation theory. Conclusion: The first chapter is a good read as it presents a historical introduction to QFT. Otherwise, one can hold off on Weinberg until after finishing Peskin. I’ve started using Weinberg as a reference for particular topics (after some background), and have found his books very useful in this respect.