Writing Singletons, Help

I have 2 Singleton example scripts (A and B)

Is there any difference in the two?

Is one way better than the other, perfomance or otherwise?

Please explain

Singleton example A

using UnityEngine;
using System.Collections;

public class gameManager : MonoBehaviour 
{

	public int score;

	private static gameManager mySingleton;
	
	public gameManager Instance 
	{
		get 
		{
		return mySingleton;
		}
	}
	
	protected void Awake () 
		{
		mySingleton = this;
		}
	
		public void SetScore (int i)
		{
		score += i;
		}
}

Singleton example B

using UnityEngine;
using System.Collections;

public class gameManager : MonoBehaviour 
{

	public int score;

	public static gameManager mySingleton;
	
		void Awake () 
		{
		mySingleton = this;
		}
	
		public void SetScore (int i)
		{
		score += i;
		}
	
}

Are Singletons better than SendMessage and GetComponent?

context, I have 3 Triggers, when an object Enters each Trigger 1 is added to that Trigger’s corresponding int variable in the Game Manager Script on a different object from the Triggers

Yes, they are better than GetComponent and especially than SendMessage.

More compact example:

public class LevelGlobals : MonoBehaviour{
  public static LevelGlobals instance{get;private set;}
  void Awake(){
    instance=this;
  }
  public int myExampleGlobal;
}

Make use of automatic accessors. They are powerful feature of C#.

Regarding performance: they are all equal but readability of both is questionable.