At Point of Entry (POE) at a USA port, the immigration officer will ask you, how long do you intend to stay in USA? ..Now this is no trick question.
If you are going for Tourism, and you are young i.e. between 20 to 55 years. It would be difficult for immigration officer to believe that you will touring for Six Months. Anything between 4 to 6 weeks would sounds feasible.
Even if you ask for 4 to 6 weeks it is more than likely they will give you a entry for six months.
However if you ask for six months, they might find that suspicious and give you entry from one to three months.
If you are going for Business, and ask for six months, the immigration officer might ask you more questions regarding what type of business needs to spend six months in usa. Immigration officer will try to judge wether you will work in usa ?
Again, if you ask for 3-6 weeks, it is still possible they will give you stay for six months.