Both processing time frame are almost same.Go to USCIS.com and check processing dates for both visa you gonna see it. May be 2 more months for Immigrant visa(I-130) than Fiance Visa(K1). So its better to apply for Immigrant visa. If Fiance visa gets rejected its gonna make more complicated. Do not take any chance just for 2 extra months. Check the processing dates I-129F and I-130.


https://egov.uscis.gov/cris/jsps/Processtimes.jsp?SeviceCenter=VSC