I-130 is the immigrant visa. K3 is a nonimmigrant visa. It takes about 9 months for a K3 and about one year for the I-130.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
The key difference is that you marry and then file the I-130/K-3. With the K-1, you only marry upon entering the U.S. on the K-1 visa.
Disclaimer: This answer is for informational purposes and does not take the place of a consultation with an experienced immigration attorney. This answer does not create an attorney-client relationship.
The difference is the status your spouse will have when he/she enters the country. If your spouse apply for, receives, and enters on a K3 visa, he/she must still apply for adjustment of status to obtain residency once in the United States and the filing fees are more costly. This is a temporary status. However, if your spouse applies for an immigrant visa after the I-130 is approved, he/she enters as a permanent resident (or conditional resident if you have been married less than 2 years) and does not have to apply for adjustment of status.
I-130s are currently taking 9-12 months and the K-3 process is taking 6-9 months but these processing times are always subject to change.
Answers on Avvo are general in nature and do not constitute legal advice; specific answers require knowledge of all the facts. You should consult with an attorney to review all the facts specific to your case in order to receive advice upon which you can reasonably rely.
You asked this quesiton before and we answered. Bottom line - ignore the K3. You do not need it.
The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter,not should it be viewed as establishing an attorney client relationship of any kind.