The I-134 for sure! The difference between the forms is based on the visa application, the I-134 is for temporary visa’s like the b1/B2, or in this case the k1(90 days to marry). The I-864 is for permanent residence applications. Remember that prior to arriving at your port of entry, you will be approved to marry within 90 days, this is a temporary visa granting permission to marry, it technically expires after 90 days. After marriage you submit AOS documents to the USCIS, which is why you’re not aloud to leave the US during that time as you technically don’t have a ‘legal status’ until you’re approved for your marriage green card. Once married you’ll apply for the marriage green card which will be a permanent visa category application and for that you will require the I-864 affidavit of support! Hope this helps!