AR has a reputation for a lot of delays and schedule changes.

Are the schedules equally convenient for you? And would the domestic airport be more convenient than GRU?

I've only flown GOL and AR on their (respective) domestic flights as a DL top tier elite. DL has a bilateral partnership with GOL while AR is a member of SkyTeam. In my case, tickets were issued by DL but I phoned both airlines in the USA, in English, to verify that everything was OK with my ticket/reservation and to pick seats. The airlines were different, but I wouldn't say that IME one clearly dominated the other.