Post-Scarcity Anarchism was my introduction to him, it's a collection of mid-life essays on a variety of early ideas that would later coalesce into his larger themes like social ecology and communalism (One of them is actually about updating Marxism). I found it accessible and exciting in the same way that Kropotkin's The Conquest of Bread is.

I've yet to check it out but I've heard multiple times that The Murray Bookchin Reader, a later collection of essays, is perhaps the best.

The Ecology of Freedom is considered his magnum opus as it's the longest and contains some of the most developed versions of his ideas, but IMO I wouldn't start with it as it's a rather dense and somewhat less accessible. For a new reader, Social Ecology and Communalism is a more succinct exploration of the same topics.