Comes down to preference, assigning the component in the inspector is probably the most “performant” but this isn’t really something whose performance you care about for a 1-time thing. You can argue that the .GetComponent called from inputs in Update would be excessive, but there was someone arguing awhile back that they considered it more readable.
These sorts of things aren’t cut & dry – it’s usually just whatever you and your team can read / maintain most easily.