If the OP returns to home country before marriage, he/she still has to adjust status upon returning as a K-1 visa holder. Then, the OP must wait for a Green Card (6 months to a year after entry).
If the OP marries, then returns home, the couple must start the spousal visa process. That can take 18 months to 2 years or so.
If OP marries, then immediately applies for Adjustment of Status, then he/she will obtain a Green Card in 6-12 months (likely). This is the fastest route to a Green Card under the current circumstances. I see no reason to think the adjustment of status will be denied.
Personally, I think adjusting status is a good, viable route since OP is already inside the US.