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.
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You asked this quesiton before and we answered. Bottom line - ignore the K3. You do not need it.
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