Books have been written on the topic, one by the person who founded this website:

Mileage Pro
By Randy Petersen, Randy Petersen and Tim Winship, Tim Winship
(I think there is a more recent book, too.)

Randy also has Inside Flyer magazine which has a monthly article rating a hotel or airline program.

Check out these elite of the elite programs:

United - United Global Services

Marriott - Platinum Plus

Starwood - Ambassador

Each is by invitation only with no public documentation on what is required for inclusion.

Thanks SanDiego1K for all these helpful references!

Are there probably any members of United Global Services or Marriott Platinum Plus on the forum that could give me some details on the associated benefits? I tried to make an Internet search, but Google does not seem to provide much reliable information on any of these.

Actually for Marriott their "top" tier is called Platinum Premier. And yes there are a quite a few of them who post in the Marriott forum. To find out more, check out the http://www.flyertalk.com/forum/marri...ier-level.html thread. The http://www.flyertalk.com/forum/marri...-new-plat.html thread is very recent and a few Plat Premier (PP) members have posted in there as well.

British Airways have Premier, which is invitation only extra tier for the select few. You won't find much about it on the BA web site, but there are threads about it on the BA forum here and a few BA Premiers post there. Warning - can be a contentious subject (for example on making the aircraft wait for Premiers)! A search in the BA forum will reveal some useful threads which will give more information.

The numbers and conclusions from that article seem pretty solid, but it seems to me that a large flaw in the whole system was assuming solely US hotel stays. That is probably why even though SPG did not make the top of the cut for that American journalist, many FTers wholeheartedly believe it's the best hotel loyalty program due to its global nature. Not to mention that extra point earning promotions will vary from year to year and need to be accounted for when choosing a hotel loyalty program.