Of the three you mentioned easily striker. If you check Pep's past teams he's never had more than two natural strikers in his squad, he had Mandzukic/Lewandowski and Pizarro (and Müller, although on the pitch he's more of a 10) at Bayern, and at Barca he had Messi and Villa/Zlatan. If injuries struck or rotation was needed he'd just play other players as a false nine there, like Pedro, Fabregas, Götze, Ribery or even Robben.
Aguero and Iheanacho are enough as is, if it's needed we can always play De Bruyne, Sterling or Nolito there (or Sané if we get him). Meanwhile a new leftback should be an absolute top priority, and if Yaya leaves we really need another quality midfielder too.
