超簡易FSM。　同じオブジェクト上なら１つしかenableにならないようにする。

FsmAIBase.cs

using UnityEngine;

public abstract class FsmAIBase : MonoBehaviour
{
	void OnEnable()
	{
		Change();
	}
	protected void Change()
	{
		foreach(FsmAIBase c in GetComponents<FsmAIBase> ())
		{
			c.enabled = (c == this);
		}
	}
}

FsmAITypeA.cs

using UnityEngine;

public class FsmAITypeA : FsmAIBase
{
	void OnGUI ()
	{
		GUILayout.Label ("type A true");
		if (GUILayout.Button ("type B false")) {
			GetComponent<FsmAITypeB> ().enabled = true;
		}
		if (GUILayout.Button ("type C false")) {
			GetComponent<FsmAITypeC> ().enabled = true;
		}
	}
}

FsmAITypeB.cs

using UnityEngine;

public class FsmAITypeB : FsmAIBase
{
	void OnGUI ()
	{
		if (GUILayout.Button ("type A false")) {
			GetComponent<FsmAITypeA> ().enabled = true;
		}
		GUILayout.Label ("type B true");
		if (GUILayout.Button ("type C false")) {
			GetComponent<FsmAITypeC> ().enabled = true;
		}
	}
}

FsmAITypeC.cs

using UnityEngine;

public class FsmAITypeC : FsmAIBase
{
	void OnGUI ()
	{
		if (GUILayout.Button ("type A false")) {
			GetComponent<FsmAITypeA> ().enabled = true;
		}
		if (GUILayout.Button ("type B false")) {
			GetComponent<FsmAITypeB> ().enabled = true;
		}
		GUILayout.Label ("type C true");
	}
}