Producers of reality television create the good (dramatic) television by creating conflict situations. With reality shows like Survivor where there is a cash prize and people vote each other off this is not needed because the contest creates these conflict situation. The voting process forces contestants who are normally fair moral people to scheme, create alliances, and then stab those alliances in the back in order to win. In the case of Survivor, they combine the stress of voting off your peers with hunger, fatigue, and dehydration. The combination of all of those things together is reality television gold.
On the other side of it there are the shows like The Real World, which is more about relationships and drama than about competition. Here they replace hunger and fatigue with excessive amounts of alcohol, and inebriated people once again create reality television gold. In either case the shows have put a group of strangers and forced them to live in close quarters for an extensive period of time.
Personally I think that any kind of show that has these elements have a recipe for success. The amount of success is more dependant on the editors because each of these shows are going to have hours upon hours of drama and what you use becomes the question.