I don't have a lot of experience running both in 3e, but I might be helpful anyway.
Scarred lands was made for/under e & 3.5e, and the
wilderlands go back to the very beginning, to OD&D. That matters in obvious and subtle ways. I'd give that as a point for Scared lands, however, it's all made for the rules used, not warped to fit from elsewhere.
While the
Wilderlands of high fantasy are indeed a "kitchen sink" (apparently the only campaigns now), they certainly aren't
Greyhawk light in the least; moreover I love
Greyhawk! No setting hooks? LOL, that's a joke; but I can get it more if one thinks of it as a half dozen setting mashed into one. The hooks are regional or a few regions. Frankly, though, alot of the cool/unique bits are pulled back from or not really rules mechanically made all that well; Red, Green, Purple, Yellow, etc peoples among them (once inspired from
Burroughs's Mars, surely). There is less materials in d20 format, far more materials from before. Some of the best adventures ever made are set here,
Dark Tower by
Jennell Jaquays, for example. If you want an urban centered game, the
City State of the Invincible Overlord is simply the best, the originals maps alone inspired countless hours of play. OTOH, the collection of random encounters that was the judges guild way back in the day isn't exactly the best directly translated to d20. 50's & 60's fantasy?
JRR Tolkien, CS Lewis, Fritz Leiber, Poul Anderson, Andre Norton, L Sprague de Camp, Jack Vance, Michael Moorcock, Anne McCaffery, Ursula Le Guin? Yes, I guess it is...as D&D is, and always has been? Sounds like the opposite of a criticism to me.
Scarred lands reads as
clash of the titans took place, but I dunno if it feels that way in play. That said, I like the premise a ton, and I agree unique monsters & terrain/weather give it great & unique flavour. I'm just now realizing the 2010 movie instead of the wonderful 1981 film might be being referenced. I'd not insult the scarred lands calling it 2010 trash, but in any case, to each their own. You will decide which suits you & your group more.
Scarred lands has much more material made specific to the edition to be played (or 3.5e). It's got several different campaigns/continents, but I only was familiar with the first (& mainly the monsters!).
Ghelspad, Mithril, city of golems, and Holowfaust, city of necromancers.
I can't agree on better written, but maybe if we are talking basic campaign book to campaign book I can? Wilderlands certainly doesn't have the monster books, Scared lands can't even begin to compete module/adventure wise (though a fair bit of wilderlands never got converted, and conversion itself is always a diminishment to some degree). Depends what you want I guess. I'm think both would benefit from a strong guiding hand DM at the outset, not a railroad, but on characters to be used (avoiding the silliest kitchen sink effects).
You could more or less just run
Dark Tower, set in the desert lands, near the holy city.
You could do an urban centered
City state game
You could make up your own stuff more centering around a given region/people. They can vary wildly...wizardly blue ice magic people on their magical island?
Avalon. Savage barbarian swordsmen? the Red
Altanians fit the bill(with the women druids & psychics).
Amazons & sabre tooth "tigers"? check.
Vikings? Shandiks. The kitchen sink is there, indeed it is perhaps the first/among them, but the focus & overlap can be fairly minimal, really. I've played in a whole, full, many year campaign almost entirely inside
Verdistan, with visits to the various neighboring areas at times, all about resistance to the
World Emperor. We started session one seeking escape from slavery, my character was a Veridian noble (aka a greenie) religious heretic/blasphemer (aka a cleric of LG
Mitra). Game went L1 to L20+. It was very specific & not too generic at all, as far as D&D goes anyway (D&D is [almost] always a bit generic).
Scarred lands offers similar in that, with plenty of cool places, often better defined in d20 terms & much more consistently linked. It's got the
serpent amphora trio of adventures, though I cannot say how good they are.
Not really answering your question, but hopefully it was helpful.