Unity3D Input: OnGUI vs.Update.

gistfile1.cs

using System.Threading;
using UnityEngine;

// [ExecuteInEditMode]
public class InputTest : MonoBehaviour
{

    private float _delay;
    private float _fps;
    private float _fpsTime;
    private int   _fpsFrames;
    private int   _clicksInGUI;
    private int   _clicksInUpdate;
    private float _guiClicksToSec;
    private float _clickInUpdateInSec;

    private const int MaxDelay = 500;
 
    void OnGUI()
    {
        // every Event
        
        var ec = Event.current;
        if (ec.type == EventType.MouseDown && ec.button == 0)
            ++_clicksInGUI; // <----

        var w = Screen.width;
        var h = Screen.height;

        GUILayout.BeginArea(new Rect(w/4f, h/4f, w/2f, h/2f));
        {
            GUILayout.Label("FPS: " + _fps.ToString("f1"));
            
            GUILayout.BeginHorizontal();
            {
                GUILayout.Label(string.Format("Delay: {0:0.#}", _delay));
                GUILayout.Label(
                    string.Format("Frame delay: [0,{0}] milliseconds",
                                  MaxDelay));
            }
            GUILayout.EndHorizontal();
            
            _delay = GUILayout.HorizontalSlider(_delay, 0, MaxDelay);
            
            GUILayout.Label(string.Format("OnGUI clicks/sec: {0:0.#}",
                                          _guiClicksToSec));
            GUILayout.Label(string.Format("Update clicks/sec: {0:0.#}",
                                          _clickInUpdateInSec));
        }
        GUILayout.EndArea();

    }


    private void Update()
    {
        // every frame

        if (Input.GetMouseButtonDown(0))
            ++_clicksInUpdate; // <----

        ++_fpsFrames;
        _fpsTime += Time.deltaTime;

        if (_fpsTime >= 1f)
        {
            _fps = _fpsFrames/_fpsTime;
            _guiClicksToSec = _clicksInGUI/_fpsTime;
            _clickInUpdateInSec = _clicksInUpdate/_fpsTime;
            _fpsFrames = 0;
            _fpsTime = 0;
            _clicksInGUI = 0;
            _clicksInUpdate = 0;
        }

        if (_delay >= 1f)
            Thread.Sleep(Mathf.CeilToInt(_delay));
    }

}