For the Form I-134, tax transcripts from the last 3 years are usually sufficient and preferred because they are official IRS documents. However, to be thorough, you can also include tax returns (1040s), W-2s, and proof of tax payments if you have them. This ensures you meet all possible requirements and avoid delays. Double-check with the U.S. Embassy in Islamabad or your fiancée’s visa instructions to confirm exactly what they need. Better to be over-prepared than under!