I would say the usage of “vai ser” or “será” is very similiar to the usage of the future with “going to” or “will” in English. So I agree with Heitor when he said that the both sentences are correct. However, depending on the place you are here in Brazil you will hear one or another more often. I can say I usually listen to “vai ser” more often in spoken Portuguese and “será” in written Portuguese, but is not a rule at all. You can also apply the same idea with other verbs. For example: Eu vou falar com você amanhã - I'm going to talk to you tomorrow. Eu falarei com você amanhã - I will talk to you tomorrow. Ele vai trabalhar o dia todo - He is going to work all day long. Ele trabalhará o dia todo - He will work all day long. In order to perform a verbal communication you can pick either of those forms. I hope it helps!

Olá Tung, as duas palavras querem dizer a mesma coisa, não há diferença alguma. SERÁ e VAI SER são corretas, mas nós usamos SERÁ com mais frequência. Hello Tung, the two words mean the same thing, there's no difference. SERÁ or VAI SER are correct, but we use SERÁ with more often.

Both "vai ser" and "será" are right. Nonetheless, if you want to be formal, "será" is the right one.