Lewy is decent, but also relies heavily on a legalistic view of the war. He's also considered one of the "old" generation of commentators on the war, and thus thought suspect by newer authors.
If you're looking for a battlefield view, Kieth Nolan is really hard to beat. He spends almost no attention on COIN considerations, though. Bergerud does, but his analysis gets thin when he tries to extend observations from one province to all of South Vietnam. Moyar and Prados are both quite political (although on opposite ends of the spectrum), and it's worth keeping that in mind when you look at their books.
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