As I read through the postings of the fine folks on here, I realize that most of you (us) spend way too much time in hotels. The general public has no idea.
I, like you, prefer the Marriott brand over all others. I also fly USAir as my preferred airline. That choice is much more territorial. Living in the Philly area, USAir is the major carrier best servicing PHL.
There are times when a Marriott property is not available to where my work takes me. I need second choices for my 30 or so nights per year this situation develops. I joined, and maintained status in Hilton, IHG (Holiday Inn), Starwood, Choice, and a little bit of Hyatt. In 2009, I decided to exclusively, where possible, use IHG as my backup. I did this for two reasons. First, IHG seems to have some lower brands available in some of the remote towns that Marriott doesn't service. Secondly, until recently, Marriott had no properties in Ocean City, MD. This is a weekend getaway town that both me and my wife enjoy. This town has many IHG properties. I figured if I maxed out my non Marriott stays with IHG, I could score a few free stays in OC. I considered Hilton as my backup, but they seem to mirror the same location map as Marriott. My double secret probation backup is Choice. They put hotels in towns that have one or less traffic lights. Sometimes, my work takes me there. Beware, these hotels are often friendly but lack anything more than a bed and a bolted down box TV.
For airline backup, I use American. I barely fly enough to maintain Silver with USAir, so my backup here was not done with any real thought.
I'd love to hear the rationale for your backups. Please share, I tend to learn more from you nice people than most other groups.