If you intend to immigrate and take up permanent residence in the United States, you may not do so using a temporary visa such as a visitor visa or visa free under the U.S. Visa Waiver Program. As an intending immigrant, you are required to wait until your immigrant or fiancé(e) visa is issued.
However, if you wish to make a temporary visit to the U.S. while your immigrant visa is pending, and then return to your country of residence outside the United States, you may travel to the U.S. on a tourist (B-2) visa, or visa free under the Visa Waiver Program, if you qualify.
If applying for a B-2 visitor visa, you will be required to furnish evidence of your residence outside the United States to which you intend to return at the end of your temporary stay. Although a pending immigrant or fiancé(e) visa application is not necessarily conclusive evidence of immigrant intent, it is a factor considered by consular officers reviewing a nonimmigrant visa application. If you are unable to convince the consular officer reviewing the application that you do not intend to return to your country of residence after a temporary visit to the U.S., the officer will refuse your temporary visa application.
When traveling to the U.S., either with a visa or visa free under the Visa Waiver Program, you should be sure to carry with you evidence of ties to your residence outside the U.S. If the immigration officer at the port of entry is not convinced that you are a bona fide temporary visitor, you may be denied entry into the United States.
Finally, any attempt to misrepresent your intent in applying for or using a non-immigrant visitor visa to enter the U.S. is strongly discouraged. Willful misrepresentation and fraud are serious violations of U.S. immigration law and carry serious consequences.