None. They are all crap.
The only one I watched that had any kind of respectability about it was a spy school one I watched recently, that was made in the UK. It followed a group of people who wanted to be spys and were going through a kind of spy school. At the end of each episode, the "teachers" sent the worst performer home. At least the contestants were decent people, and not moronic idiots like those in big brother, idol and survivor.
Idol makes me laugh actually. Fans spit and scream when their favorite is kicked off the show, not realising it doesn't matter one zot who they vote for. The winner will be the person the record companies decide will sell the most records. The public voting is a big con designed to keep people watching, ratings high, and build an early fan base for the winner to make money.
Big brother is just plain the biggest load of crap I've ever tried to watch (lasted about 20 minutes). That show is made to appeal to 13 year old girls, how anyone more mature could find anything good about it is beyond me.