Depends on what you're after.
Spellbound - of the three, this one is the most sparse. I like FR6 Dream of the Red Wizards better. The box is huge but the books are slim and the borders broad. It details Rasheman, Thay, and Aglarond, although not nearly to my liking. Never really held my interest for very long.
Netheril - man this one is frustrating. First thing to note is that its set in the past, at least a good 2,000 years or so prior to current DR. Secondly, magic is higher power, with spells going to 11th level (and one 12th level spell). The setting of Netheril is fun to read, but man it does not line up with FR lore at all. Hell, half the reason I wrote "Mystryl's Harbor" was as a way to use the Netheril boxed set in a way that didn't completely wreck FR lore on Netheril. The rules aren't particularly great and the magic is ignorable. It never really addresses the "um, we have floating cities. We can pretty much go anywhere we want" aspect of the setting. I think I'd just use it as a normal setting, on its own, disconnected from FR, with a twist of having floating cities around ran by a handful of really powerful, almost alien wizards.
Lands of Intrigue - by far the best box, just by authors' rep alone. It details Amn & Tethyr at about the time Amn gets wrecked by a rising humanoid empire and the Tethyr civil war comes to an end. Of the three listed it is the most useful, IMHO, for running a fairly standard FR campaign. It pairs well with Empires of the Shining Sea, as the two were written at around the same time so they are very consistent between the two.
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