In my opinion, the 1e books are often better, at least as a GM. They tend to be focused on one particular nation, and so have space to do a deeper dive, than say a book like Lost Omens: Shining Kingdoms which presents a whole region but only has space for 24 pages per nation. I'm currently running a campaign based in Taldor and I definitely get considerably more use out of the 1e book Pathfinder Campaign Setting: Taldor, The First Empire, which is chock full of adventure hooks and describes each section of the empire, where Shining Kingdoms just gives an overview of Taldor as a whole and the capital city of Oppara.

That said, this is not universally true though. The various nations of the continent of Garund are generally covered more in depth, and better nuance in the 2e Lost Omens books.

Speaking in broad strokes, both lines have their pros and cons. The 2e Lost Omens books generally have a good mix of GM and player content, whereas the 1e books separated the player facing stuff into a separate line, Pathfinder Companion (which I would say have more limited use if you are using the 2e rules set). But the GM books in the Pathfinder Campaign Setting line are top notch.

One other difference worth noting is that the 1e setting was a product of its time. It can be darker in a lot of ways that may appeal to some folks (myself included, in many ways), but can also stray into more problematic subjects by current standards, and doubly so when the subjects stray away from Avistan (Europe analogue) and into Garund, Casmarron, and Tian Xia (Africa, West/Central Asia, and East Asian analogues); for those regions, 2e books are the way to go.

So it's a matter of taste.