Another long information post. Here are my general impressions for those expats in the planning stages.
"LUXURY"
Arizona
I've blogged about this one before. I think most people agree that this is the most attractive looking compound to stay in, with its lovely 'ranch' style decorations, a beautiful resort style central pool, and its golf course and driving range. And its horse. It's really one of the best compounds with a pleasant atmosphere, but it has a matching price tag for pockets that run deep.
Cordoba & Al Hamra
Sister compounds with a common owner, Cordoba and Al Hamra are very large compounds. Cordoba is supposed to have some of the most spacious villas in Riyadh, with beautifully maintained grounds and a very good maintenance team. Cordoba can sometimes feel a bit cold as there is less of a community atmosphere there than on other compounds and it has a truly terrible compound restaurant.
Kingdom
Kingdom is famous amongst women for its coffee mornings. It has a wonderful looking central pool with fake rocks and boulders everywhere, a nice cafe area and restaurant, and even has a birdcage on display full of parrots and budgies. I've never been in a villa but they are supposed to be quite nice. This compound has the longest waiting list in the Kingdom because its prices are reasonable for the quality of accommodation.
Eid
This is a smaller compound in comparison to others on this list, but still sizeable. Grounds are well maintained, and Eid boasts a wavepool and a fairly decent restaurant. Villas tend to be on the smaller side compared to other compounds in this price range, but what people tend to like about Eid is the friendly atmosphere.
Jadawel is supposed to be another nice compound that has very spacious residences. I've never been there but I hear it's great. One drawback about Jadawel is its location twenty minutes from the edge of the city.
"MID-RANGE"
Arab Investment Compound
A smaller compound near the diplomatic quarter, this one is quite nice and cozy. The villas we've been able to visit are comfortable and residents seem content with it, but you don't see the same kinds of sprawling set ups as in the luxury compounds. A lot of people like its location, that is relatively central for a Western compound.
Al Yamama
There's actually three Yamama compounds now, but I've only been to Yamama 2. These compounds are large and seem to have a decent number of amenities too. The villas I've seen in Yamama tend to be fairly simple bungalow type houses made of concrete blocks but they are generally spacious enough.
Wadi
A smaller compound, this is a decent looking place, and has enough amenities to make your stay reasonable. As with others on this list, this compound is well kept with all the amenities you would need and our friends there seem content with it.
Arabian Homes, Nadj, and Villas Rosas are also smaller compounds that are well maintained from what I hear.
"BUDGET"
Seder Village
Ahh...Seder Village. This is a compound that everyone knows and talks about and you'll see why when you get here. Housing is bungalow style, but it's a notch below Yamama; the construction of homes is nowhere near the Luxury compounds. The thing that sets Seder apart from others is its fun & social reputation - it is supposed to have a solid community of expats that are plugged into events in the region, and is a popular choice for singles.
Ranco
Ranco's residences range from motel-style apartments to larger villas. Not much to say about their rec center or amenities, just that they're there, and they get used. Their prices are fixed at very reasonable rates.
Fal
I understand that Fal is a military facility that has been converted to a compound. The rooms are very small and sterile, however the place is cheaper than most.
HERE are some recent prices of some of the compounds that I've mentioned.
IN SUMMARY...
In a luxury compound, you can expect resort-style surroundings and extra amenities on large compounds, beautiful villas, ever-increasing prices, and lengthy waitlists. To get into these highly sought-after compounds, you usually have to have a friend living at your preferred compound that is willing to vouch for you and introduce you to management. Many long-timers have left them in recent years because the pricetags have doubled within the span of the last 5-10 years.
Mid-range compounds usually have most of the necessary amenities on their compounds to make living there comfortable and easy, well manicured grounds if not sprawling ones - maybe no wavepool or bowling, but a hairdresser and a nice gym. On the budget end, you'll have the basic amenities that are convenient in a compound, but not necessarily the nicest looking houses or grounds.
When it comes to demographics, each compound is different, and you have to make a visit to the compound in question to really get a feel for what types of people live in each one. Many Westerners feel uncomfortable in compounds that have large arab populations because of the cultural clashes that can occur. If your housing is not provided by your employer, the best thing to do is to take colleagues & acquaintances up on their offers for you to go visit them at their compounds, and plan a stop at the manager's office. Phone calls and emails will generally not get you into any of the higher end compounds.
Good luck to you all, and hope this helps!