Vince
Do you know or have a feel for how long the K-1 VISA takes versus the K3?
Alton
I believe they are only months apart (like 3)? It's always changing. They say "This visa takes BEST SPEED MINIMUM four to six months processing time" but it's more like 8 to 11? Depends on how they feel??
The main reason people who are K1 eligible consider the K3 process is that they believe the K3 visa will process more quickly. Even if USCIS happens to be processing K3 visas faster than your regional USCIS service center is processing K1 visa petitions at a given time, any apparent advantage in K3 visa processing times is usually deceptive. In theory, a U.S. fiancee can start a K1 visa petition immediately, provided they have all of the necessary documentation. To even start the K3 petition, they would have to get married outside the U.S. Unless the U.S. citizen is prepared to take that step and already has made travel plans, it could easily be several months before they will be able to start the K3 process, and the delay could more than wipe out any K3 visa processing time advantage.
In addition, before you can file a K3 visa application, you will need to be able to show that you filed an immigration petition with the USCIS service center that serves your region. This can easily add several weeks onto the process, while you wait for an official USCIS receipt or equivalent proof that you have filed the immigration petition to arrive.
Finally, the processing times at various service centers are not static: they can change greatly over time. It is entirely possible that, by the time you start your K3 visa application, either the service center that would have processed your K1 petition will have reduced its backlog, or USCIS will have fallen further behind in processing K3 applications (this seems especially likely if a lot of people decide to use the K3 process when they could have used the K1 process).
For all of these reasons, it is usually better for those who are K1 eligible to stick to the K1 process, and leave K3 visas to those who are already married. However, as noted above, every case is unique.