So long-range mobile artillery with heavy armor would be the best arty in your opinion?
What about anti-air? For me it would have to be heavy AA since I want to to cover other formations. Or maybe its better for every formation to have its own native AA ability.
I have to state though that neither side was fortified in this fight so losses was very high on both sides... but during an attack you are not likely to have any fortification to start with anyway. For each Heavy Vehicle, heavy armour with dual MBL a defending garrison could afford 9 artillery pieces in simple light armoured emplacement with a minimum of 6 fortification. So having your artillery survive that onslaught can be quite important.
For AA you can go with both light, medium and heavy in formations. I generally put some light AA in all formations medium in support and then heavy in rear formations if I have heavy AA researched. light AA will give some defensive capability to support formations if they are attacked and soak some damage and they protect to some degree against air attacks. If there are no enemy air you can always move most of the AA to the front-line units after a while... I tend to do that with medium AA as well but rarely with heavy AA as they are to expensive to risk at the front unless I'm outmatched and need every gun I have on the front line.
I have a typical mobile infantry brigade that is 30.000t in size which have 15 HAA, 30MAA, 45LAA in total. I probably could have run with more LAA guns and often do, but this formation was restricted to be carried in a 30.000t fast response assault ship for rapid and light deployment. This is not a heavy assault formation but more of a rapid response force for defending colonies that is being attacked as quickly as possible. So, it is mainly infantry and light vehicles.
This particular formation is a Brigade with the HQ holding 15 HAA. It has three combat battalions, one cavalry company and three fire support companies. Every formation have 5 LAA each and the fire support companies 10 MAA each.