Question: "ang magiging" vs "ay magiging"

"Ang" is definitive unlike "ay".
1 = That is the prize that will be ours!
2 = That prize will be ours!
3 = That will be our prize!
Notice that 1 gives an emphasis to "that" (the prize) because of the definitive article "ang". There's no difference aside from that. But in casual settings, they become the same thing when roughly translated [That prize will be ours!].

@DenC Thank you for distinguishing them! Which of the 3 would you say is the most natural in speech since they do essentially all mean the same thing?

@NovaChromatic For me, they have the same meaning but they differ on the intent. 1 sounds natural when you're aiming to show what the prize is or when there are several things that can be the prize and the one you're showing is what you want. Meanwhile, 2&3 is when you want to somehow boost the morale of, say for example, your team. Because it's like you're claiming the prize as yours already. In that regard, I'd say 3 is more natural and uplifting than 2.