Marco is spot on, in saying that the answer depends on your architecture, and what follows is good advice, on how you should approach towards the 'right' answer.
Extending upon what he said; one should also consider whether there are any intermediary API calls before you return a result. If these API calls are to third party services, which have rate limits on the number of API calls one can make; in such instances, the "1 JSON" return would be preferential.
To conclude; quoting Marco —
...decide for either based on facts, not on advice and speculation