One of the Disadvantages of the Get Component Cached approach is that when you look at it in the Inspector it gives no indication that it needs a Rigidbody to actually work. So this approach simply adds a [RequireComponent attribute to the class so that Unity will automatically add a Rigidbody when you add the RequireComponentExample component and won't allow that Rigidbody to be removed first.

using UnityEngine;

[RequireComponent(typeof(Rigidbody))]
public sealed class RequireComponentExample : MonoBehaviour
{
    private Rigidbody _Rigidbody;

    private void Awake()
    {
        TryGetComponent(out _Rigidbody);
    }

    private void FixedUpdate()
    {
        _Rigidbody.AddForce(Vector3.up * 10);
    }
}

Advantages

Unity will automatically add a Rigidbody when you add the RequireComponentExample component in the Inspector.
Same runtime performance as the Get Component Cached approach.

Disadvantages

Summary	Description	Solution
Verbose	The `RequireComponent` attribute makes the code quite a bit longer than the other approaches and means that the `Rigidbody` type is repeated twice.	All other approaches are better in this regard.
Inflexible	The `RequireComponentExample` needs to be on the same `GameObject` as the `Rigidbody` unless you edit the script.	Serialized Field.
Hidden Dependency	Looking at the `RequireComponentExample` in the Inspector gives no indication that it actually requires the `Rigidbody` unless you actually try to remove it.	Serialized Field.
Manual-Only	The `[RequireComponent]` attribute is enforced when you manually add the `RequireComponentExample` component using the Inspector, but not if you call `gameObject.AddComponent<RequireComponentExample>();`.	None of the other approaches really solve this one, but Serialized Fields make the requirements clear if you simply look at the Inspector.

Require Component

Advantages

Disadvantages