Regarding availability and airline preference: I've received whatever airline I've requested. And since it's a paid ticket, I haven't had an availability problem.

Having said that, think twice before using your miles for an airfare. Here's why:

A $600 ticket cost 28,000 Value Miles, or a redemption rate of 2.14 cents/mile.

But if you look closely at your membership info, you'll see that you can get one night at many Ritz-Carlton hotels for 12,000 miles. Ritz rooms can start at $350.

So if you use 12,000 miles for a $350 room, your redemption rate increases to 2.9 cents/mile, or a 36% increase over the airfare rate.

Keep in mind that the 12,000 miles will get you a night at Ritz's resorts like Amelia Island, FL, where the rates can be much higher than $350.

Another way to compare: 60,000 miles will get you a $900 ticket or five days in a hotel (which cost much more than $900).