Almost always a tradeoff of price and service. I book through a HAL PCC and get very good service, many times "over and above". Have gotten some great deals due to her "making a call".
Good example, in Dec I was wanting to upsell to a Neptune from a Signature, but Neptunes sold out (6 weeks prior to sailing). My PCC called the upsell department and informed them that I would like an upsell if one opened up. The day prior to sailing (at 5 pm) I get a call from the upsell department offering an upsell to a Neptune (someone had cancelled that day). My cost was a REFUND of $1 (long story why). Try this with most TAs or big box reps.
DO I get the lowest price on my cruises? Probably not, but by working with a good PCC the overall deal for me is often better. Many times my PCC has gotten me refunds or perks that I never thought she would be able to. Further, I seem to be able to get upsells to a Neptune on 80-90% of our cruises, at a great price by the way.
So, I guess that my answer to this question is that how to book a HAL cruise depends on how involved you are and if you can find a good PCC.