Ata (may Allah have mercy on him) says: I asked Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both): "Should we recite «وَاتَّبَعُوا» or «اتَّبَعُوا»?" He replied: "Both are equal, recite whichever you recited first."
Hadith Referenceسنن سعید بن منصور / كتاب التفسير / 203