I don't think that heat or electric stress is important.

I arrange them by use.

My main panel has a group of breakers for subpanels, a group for the HVAC, a group for large appliances, a group for the exterior, and a group for the garage the main is located in. There are empty spaces between the groups.

There are subpanels for my detached shop, the west bedrooms and baths, the living and kitchen, and the east bedrooms and baths.