If we’re talking strictly damage points, ST. Only the damage dealt to Ibaraki counts towards the points.
AoE, of course works well to clear out the hands accompanying Ibaraki though this will allow her to take two attacks per turn, something which previous experience has shown to be fatal at times since she hits hard and crits hard.
If you bring an AoE Servant, it will have to be someone who can also deal great ST damage (Gil is a good choice as is Raikou) so they can keep beating down on Ibaraki.
Speed is key here. The faster Ibaraki falls the better. Unlike last year though, you actually keep the damage points even if you lose the fight so that’s one less worry. Last year we had to stay alive if we wanted to keep the points we earned.
As to the other enemies, the main story isn’t an issue since they tend to be weak, as is the case in many events. But the mobs for the raid will change classes depending on event story progression. Ibaraki, however, will always be a Berserker.