Results are as expected. Async comes with a slight overhead because of the event loop, but has many other benefits. So unless you know you won't need it, go for async.

node-child-process-perf-sync-vs-async.md

Measuring sync vs async child processes in Node.js

• macOS 10.12.3
• Node.js 7.4.0

childProcess

const childProcess = require('child_process');

console.time('sync');
childProcess.execFileSync('networksetup', ['-listallhardwareports']);
console.timeEnd('sync');

console.time('async');
childProcess.execFile('networksetup', ['-listallhardwareports'], () => {
	console.timeEnd('async');
});

sync: 25.707ms
async: 39.501ms

execa

const execa = require('execa');

console.time('sync');
execa.sync('networksetup', ['-listallhardwareports']);
console.timeEnd('sync');

console.time('async');
await execa('networksetup', ['-listallhardwareports']);
console.timeEnd('async');

sync: 25.263ms
async: 45.735ms