Well, I certainly don't disagree with any particular aspect of your post, but to defend Marriott a bit...

I have participated in all 3 of the big hotel chains over the course of the past 5 years. I started out 100% Marriott in the 90's when Marriott Rewards was the only hotel program I knew of. I switched to Hilton in 2001-2002 when I was doing a few roadtrips and 12 Hampton-nights provided more than enough points for two free weeks in Hawaii, thanks to promos-upon-promos. Finally, I went Starwood with all of my credit card spending in 2003-2004.

Depending on what you want out of your hotel chain, any of the three can be optimal for you. For example, Marriott is extremely competitive in terms of their points values and redemptions if you are a family traveling with children, thanks to three family-friendly brands (TPS, R.I., and SHS) almost always in Cat 1 through Cat 3. Hilton seems to have the best top-tier: if you are a road warrior and do a lot of business stays, you won't have any complaints about Diamond status. Starwood is clearly the best for the credit-card user who doesn't necessarily log a lot of qualifying room-nights.

As for Starwood's 5th Night Free, I think that's a great award. But...HH uses 6 nights in their ALONs and Marriott uses 7 nights in their big packages. So each of them provides a "discount" if you do the "featured" stay length. Whether you like 5, 6, or 7 is personal preference (but I do give slight props to SPG for making it a shorter length.)

As for availability, I have had minor complaints with all three, but no major complaints with any of them. I've gotten my free weeks (2 each from MR and HH) in Hawaii when I wanted them. I've gotten a free Hilton room in downtown Cincinnati the night before the Flying Pig Marathon when SPG.com was showing all "standard" rooms as sold out. I've usually gotten my Cat 1 cheapie weekend rooms from Marriott when I've wanted them.

Starwood's "any room available is yours" policy is frequently gamed by the hotels to avoid giving out free rooms. In that Cincinnati case, there was plenty of inventory available for "nonstandard rooms" - or I could go to Expedia and book a standard room out of wholesale inventory. The hotel wasn't really sold out, but they crafted the system to avoid giving out award rooms. So I roughly consider the three chains equal on the availability front: they all know how to play the game to prevent giving you a free room at peak times. If anything, Hilton gets the nod here because their beta system seems really, really loose - even for non-Diamonds. (Yeah, I'm sure they'll fix that. )