To determine who is savage and who is civilized in this play, it is first necessary to come up with a definition of "savage" and "civilized" that can be applied universally to all the characters in the play. Shakespeare often found civilized behavior to be merciful, compassionate, honest, and just, whereas he condemned mercilessness, cruelty, treachery, and unfairness.
Categorizing characters as civilized or savage based on these character traits will present some problems, so let us begin with characters who are easier to slot into one category or another:
Civilized: Miranda, Ferdinand, and Ariel would fall fairly clearly into this category. All three are basically merciful, compassionate, honest, and just. Ariel engages in some deceptive and manipulative behavior, but this is because he is controlled by Prospero.
Savage: Antonio, Prospero's treacherous and unrepentant brother, Sebastian, and Stephano are clearly treacherous, merciless, cruel (or willing to be cruel) and unjust characters.
Prospero, Alonso, and Caliban are problematic characters. Prospero redeems himself at the end of the play by his acts of mercy and forgiveness, but we cannot forget that he learned everything he needed to survive from Caliban. He then enslaved him, which Caliban rightly sees as treachery. Prospero also engages in a good deal of unkind and manipulative behavior before his turn to compassion at the end.
Likewise, we can feel compassion for Caliban because Prospero has enslaved him and treats him unkindly. On the other hand, Caliban does want to rape Miranda and tries to involve Stephano and Trinculo in a treacherous plot to kill Prospero and rape Miranda.
Alonso participates in treachery against Prospero but then repents and asks for forgiveness, showing his civilized side.
We read Shakespeare because he creates problematic characters who, like real humans, are a mix of virtue and vice.