http://www.visacoach.com/k1fiancevs...
Choosing between the K1 Fiancee Visa or the CR1 Spouse visa is a difficult choice for most couples. Here the VisaCoach explains the process, in detail, along with answers to the following questions: Which visa, K1 visa or CR1 visa, is easiest? Which visa, K1 Fiance Visa or CR1 Spouse Visa, is best? Which visa, K1 visa or CR1 visa, is fastest? Which visa, K1 Fiance Visa or CR1 Spouse Visa permits foreign partner to work sooner?
To bring your foreign partner, fiancee or spouse to the USA you need to navigate a complicated and difficult immigration system to obtain permission to enter and remain in the USA. Here we describe the process for the two immigration paths that are available to you, either marry, then apply for a CR1 spouse visa for your new spouse, or propose marriage, get engaged to marry,then apply for a K1 Fiancee visa for your new fiancee.

How to bring your Fiance or Spouse to the USA on a CR1 spouse visa, or K1 fiancee visa.

Both processes are roughly the same. We prepare an application, it is submitted in the USA to the United States citizenship and Immigration service (USCIS),

And then once USCIS has completed its review, the case goes to the US State department’s
National Visa Center (NVC) in New Hampshire.

And finally NVC couriers the case overseas to the appropriate US Embassy for the
inperson interview and approval of the Fiance visa or spouse visa.
Then your partner use the K1 visa or CR1 visa to travel to and enter the USA

My philosophy, and I religiously follow with every case, work on, is that success, final outcome, final approval, depends 99% on the quality of the initial application that together we prepare and submit. The quality of the work we accomplish at the start, at the "front" of this process, determines the ultimate outcome. Quality goes in, and a positive result comes out.

K1 Fiance Visa applications go to Dallas Texas, CR1 Spouse visa applications to Dallas, Chicago or Phoenix..
After initial sorting then the applications are assigned and forwarded to one of six USCIS service centers that are scattered throughout the USA.

At the USCIS service center your case is reviewed and processed.

And the review includes an FBI background check.

When USCIS is satisfied with your application, they "approve", at least their part, then
hands your case over to NVC, based in New Hampshire.

NVC holds Fiancee K1 visa applications only briefly. They briefly touch the application just enough to confirm which consulate is the correct one to process the case, and if the consulate is current on their workload, immediately ships the case to the consulate using diplomatic courier.

While NVC only briefly touches a K1 Fiance Visa Case, for a CR1 spouse visa application NVC really gets involved. NVC asks the spouse visa sponsor to pay an affidavit of support and the consulate interview fee, and requires copies of all civil documents, police clearances and the US sponsor’s financial evidence.

NVC reviews all of your materials, and once satisfied that all is correct ,
contacts the overseas consulate, and books the next available interview date.

So at this time, both the Fiance Visa and Spouse Visa cases have arrived at the destination consulate.

As mentioned already, if your case is for a Cr1 spouse visa, the consulate interview has already been scheduled and the interview fees paid.

But for a K1 Fiance visa, it is up to you and your fiance to pay the interview fees and book the interview
directly yourselves.

But before the Interview your partner must go to a medical clinic appointed by the consulate
to undergo a thorough medical exam.

During the interview, the consular officer must be CONVINCED your relationship is bona fide
and not a sham contrived for immigration purposes.

Sorry, to say this, but US immigration has had a long and troubled history with fiance and spouse type visas
Their experience has not been a good one.

Even proof of being lawfully married is not enough.

Basically the officer must rely on the couple’s sworn statements that their relationship is a real one, not a sham in order to issue the K1 Fiancee visa or the CR1 spouse visa.