"What benefits does the spousal visa have over the fiancé visa?”
The spousal visa has a number of benefits over a fiancé visa. First and foremost, it comes with a lawful permanent resident card, which is the green card. What that means is, once the foreign spouse enters the United States, they’ll receive the green card within six months. With that green card, they’re able to travel and work.
In the long run, the spousal visa saves you some government fees compared to the K-1 visa and it might save you a little bit of time, too. Now, it does take a little bit longer in processing time upfront, but not too much longer.