Spawn different obstacles

Hello, i got this script that is spawning obstacles but is just spawning the same prefab every time and i want to randomly spawn other obstacles to! here is the script i am using:

 public GameObject barGroup; //bargroup,contains 3 bars left and right

 public float distanceBetweenBarGroups;

 Transform playerTransform;



 void Start()
 {

     playerTransform = GameObject.FindGameObjectWithTag("Player").transform;

     OnGameStart();


 }

 float lastPlayerPosition;

 void Update()
 {


     //if player player somes 6 units distance from its last distance ,then we will create new bar group
     if (playerTransform != null && playerTransform.position.y - lastPlayerPosition > 6)
     {

         createNewGroup();
         lastPlayerPosition = playerTransform.position.y; // to store the present ball position y .
     }




 }

 int groupIndex = 1;
 void createNewGroup()
 {

     GameObject barGroupNewInstance = GameObject.Instantiate(barGroup) as GameObject;

     barGroupNewInstance.transform.position = new Vector3(-5.21f, distanceBetweenBarGroups * groupIndex, 0); //this will create new bars group

     groupIndex++;
 }

 void OnGameStart()
 {
 
 }

you are a boll that if you tap the screen it will flap and its gonna continue like that and obstacles will spawn up.

please help me! :)