There are many different options to choose between when considering migration to the USA. Many different types of visas exist which apply to a variety of people and situations so some research into the details of each one is strongly recommended.
L1 visas are for non-immigrants and are generally for around three years in the United States. These are typically given to employees from companies overseas who also have a preexisting or new office in America. The spouses of workers who also move to the United States are allowed to work with no limitations for as long as the spouse with the L1 visa is in the country.
K1 visas exist for the fiancé of someone who is already a United States citizen to come into the country. This type of visa exists as long as the couple is unmarried and can be easily transferred to be a Green Card (a document which makes the holder a legal resident of the United States).
Another category of the K1 visa are called K3 visas and allow a foreign spouse of a United States citizen to enter the country. When the spouse enters the United States they are not considered immigrants and can be considered permanent residents by filling out a few specific forms.