Efrem is right that it all depends on what you want most, and your abililty to earn miles.

I have business associates who travel a lot and, in addition, are able to rack up several or many hundreds of thousands of miles in business expenses every year. For those folks, using miles to fly first class (even domestically) is a necessity of sane survival.

For other folks who have to work hard to accumulate even 100,000 miles in a year, through all sources, using those miles for a business or first class ticket to their most exotic dream destination makes a lot more sense.

Or, if you have lots of miles, and hate to fly, maybe the best thing to do is give them to friends, relatives and countrymen, if (of course) you don't happen to be gifted with flying offspring to gobble them up like M&Ms.

Or, if you happen to be an old lady like me, longing for the serenity of your golden years, you can sock them into a FL-IRA and plot nefarious unannounced visits to your children and grandchildren when you are a batty old wo(man) who has nothing better to do than golf, play bridge, hang out on Flyer Talk and drive your descendants crazy. For these trips it is possible that trading in miles for totally outlandish and embarrassing outfits that cause grandchildren to cringe as you deplane, would be appropriate and fitting.

To each his/her own.