3rd edition have the most dragon books to scour through. The Draconomicon, Races of Dragons, Dragons of Faerun, Dragons of Eberron, Dragons of Krynn, and Dragon Magic, all were books I have read through multiple times for ideas.
4th edition had some of my favorite lore for dragons, added many more members to the Chromatic and Metallic line up, and also introduced the Catastrophic Dragons which are some of my favorites. I also enjoyed their stat blocks and abilities. I love both of the Draconomicons released in this edition as well.
5th edition added quite a few interesting things for dragons in Fizban's, such as the origin of the First World, the idea of Dragons being tied to the Materiel Plane, Dragon Sight/Echos, Draconic Gifts, an interesting origin story for Tiamat and Bahamut that I found compelling and tragic, and so on.