Confused, which process makes the most sense for my situation K1 or K3 ?

[JWN440]

I am a U.S. Citizen and My fiancé is Colombian. She has a 10 year B1/B2 visa and spends 4-5 months a year here in the US. We have decided to get married and for logistical reasons would like to proceed in the most efficient manner. I called USCIS twice and received different answers each time. The first time they said used the K1. The second time they advised me to use the K3 as we should have no problem establishing the sincerity of our relationship. The K3 process seems simpler so we are considering flying to Vegas, getting married and entering the K3 process. My fiancé has two sons 17 and 18 in school and soon in college so she would like to freely travel back and forth between the U.S. and Colombia during the process. Does this sound like a reasonable plan ? Is there a better way to proceed? From experience, which process is currently quicker?

Thank you
Jim

[JWN440]

Update : 1

I'm hearing that the K3 process no longer used and what I would actually be entering is the CR1 process.

Advice?