As RHCP stated, a mix between the two sizes(as well as a mix of other things as well) is by far the best, it provides the versatility required to react to a variety of situations.
Also, luck shouldn't be discounted, getting -30% luck on a huge nuke like that would suck hard, although it's still possible with several nukes (just ask basil when he killed half my LS with almost every nuke getting over -20% luck) the chance of it happening is much lower so you can just throw 2-3 ls fleets at a target and more reliably expect the harbour to be clear.