So, if he is not very urgent to enter US, immigration visa is the better choice.
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K-3 visa processing normally is faster than immigration visa for a few months (normally 3 to 4 months faster), but your spouse needs to file I-485 to get the green card (which takes times and more money) if he uses K-3 visa to enter US. Whereas, if he uses immigration visa to enter US, he becomes the green card holder immediately after he enters US (no extra process and save a lot of money).
So, if he is not very urgent to enter US, immigration visa is the better choice.
So, if he is not very urgent to enter US, immigration visa is the better choice.