postgis/haversine accuracy: which one is best?

I'm having an issue with calculating distances.

I have installed postgis, and I'm saving Lng/Lat points in the database

CREATE TABLE geo (gid serial PRIMARY KEY, geo geography)

For inserting a record, this is what I do:

INSERT INTO geo (geo) VALUES (ST_MAKEPOINT(Lng,Lat)::geography))

When I do the following query with some Lng/Lat variables, I get the following output:

SELECT gid, ST_DISTANCE(geo, ST_MAKEPOINT(Lng2,Lat2)::geography) FROM geo;
----
OUTPUT: 1    424.02930940m

Secondly, when I do the exact same calculation with the following formula (haversine formula in javascript), I get a slightly different output.

/*
const coords1/2 = {
  lat: // latitude,
  lng: // longitude
};
*/

export const haversine = (coords1, coords2) => {
  var R = 6371000;
  var x1 = coords2.lat - coords1.lat;
  var dLat = x1.toRad();
  var x2 = coords2.lng - coords1.lng;
  var dLon = x2.toRad();
  var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(coords1.lat.toRad()) * Math.cos(coords2.lat.toRad()) *
    Math.sin(dLon / 2) * Math.sin(dLon / 2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var d = R * c;
  return d;
};
----
OUTPUT: 422.20392010m

It's a difference of 2 meters, but I need the most accurate of the 2. It's for an app for geocaching.

I'm currently using the haversine formula in my app, but I'm thinking about switching to postgis because it would simplify my queries a lot.

Which one can I rely on the most?