Hello songsparrow,
Kim and I went through the similar thought process

it's only normal to figure out your options. Why did we come down to the K-1 route? For a few reason but the major factor is that: If you choose to go with the K-1 Route, you only have to deal mainly with the US Government, which compared to VN Government is 1000 times EASIER and 99% corruption-free!
If you choose to go the other route, you must prepare to pay out a lot of money for the Vietnamese Government Officials in ALL LEVEL of the process, and the wait is LONGER for no good reason from the VN side. Even if you try to ask for some information, it will cost you money for them to answer your inquiry.
Just make sure you weight your options out, who do you want to deal with during this coming stressful times: US Government or VN Government?
One more note, even after you married your lover in VN, now you have to go back to deal with the US Gov., for your K-3. Why double trouble yourself?
Just some of my opinions
Good luck and no matter which route you choose there are some cool people on this board can help you out...
love chuck and kim