I asked this question to a lot of question sites, such as Yahoo! Answers. It's just sad that none answered my question. People should care more about fonts since wrong choice of fonts are usually the source of ugliness.

Silly me, I forgot the link! Here it is. http://flic.kr/p/bR2fsR

Helvetica Neue : it's a reworked version of Helvetica, common and mainstream.
Myriad Pro : for Apple fanboys !
Nanum Gothic : impersonal font look like Myriad pro, Frutiger...
Segoe UI : Hmm... good but isn't the best !

As always, depends on what you want to use it for, which environment and what audience. In short, your question is far too simple. You don't choose a font. You choose an effect you want to achieve, with whom, and then you pick the font that will do the job. It has nothing to do with liking one font over another. It has to do with achieving a goal. Why not talk with your type director.

For a normal document, just the text on it.

You can use all sans serif or serif fonts except Comic Sans MS.