The damage between starting with the Magical rotation (unbuffed Goring Blade into Requiescat -> Holy Spirit) and the Physical rotation (Goring Blade -> Royal Authority combos while under Fight or Flight) is pretty small. If anything, I'd say it depends on the fight mechanics. If it's a boss that requires you to move around a lot very early into the pull, the Goring Blade under Fight or Flight would be the better starter since it and Royal Authority can be done while staying mobile. If it's a fight that lets you sit in one spot at the start of the pull for a decent chunk of time, the Magical Rotation would be the better option.