Presente Indicativo: Presente
(yo) prefiero
(tú) prefieres
(él/ella/Ud.) prefiere
(nosotros) preferimos
(vosotros) preferís
(ellos/ellas/Uds.) prefieren
Common types of stem-changing verbs include: o ---> ue and e ---> ie.
Because Preferir ends in e and it is an Ir verb we need to change the stem because of that. So it stays -ir.