[jiggy2011]

I think this basically boils down to: "are you likely to have many users connected concurrently at any one time"

If your API basically involves a client connecting, quickly getting a small JSON/XML response and then disconnecting again you are probably absolutely fine with Apache unless you have truly enormous numbers of users.

OTOH if the socket is likely to be held open for a while, because maybe the API responses can take some time to be returned or the client is likely to hold the connection open in order to get a stream of data over time then you may get more mileage out of nginx.

[zerop]

service returns quick & short JSON responses and huge number of users are going to hit it. So basically there are going to be enormous concurrent connections each returning quick and short json response. No heavy work by each connection, just that there are too many.