I agree with Sail. She's been on many HAL cruises and is an expert on this subject. She's also correct on the guarantee dilemma. If you want to avoid certain areas of the ship, you should always book a specific cabin.
Me, I do it all different ways but am willing to accept some guarantees. This last one turned out fine but I understand that may not always be the case.
Good luck with your next cruise. Hope it's better for you.