They both have their own problems... but I think overweight is worse. Even with added health problems... people can still see how overweight you are, where as you can't really see if someone is underweight if they are wearing... er, clothes.
Overweight, mainly because i am, but thats beside the case. With being underweight, that can be solved by just eating a normal 3 meals a day. Overweight has to be solved by weeks of exercise, or weeks of dieting, or expensive pills, or expesive specialty food (youve seen nutrasystem), or expensive surgery. Plus being overweight your publicly reminded of i everyday by not only youself, but TV, other people, and various forms of communication. Plus who do you see going on more dates and getting more relationships, and overweight person or an underweight person. Now granted both not overdone isnt a problem, but often overweight people seem to have more health problems. But one thing to look at and think about, who seems like a happier person, an overweight or underweight person.