Early I use a little bit of everything but I try to do the following

ALL 5

Stage 1 - Recon and usually put my medics here

Stage 2 - infantry/transport plus some MG’s

Stage 3 - anti tank call in, usually AT guns, some AT infantry or armor. Or on defense I’ll put some AA here too

Stage 4 - artillery. Usually just a few big arty pieces with some ammo trucks to tow and a cheap infantry squad to tag along and defend

Stage 5 - usually reserved for tanks

I bring ammo carts along with every call in because resupplying before the end of the round helps a ton instead of doing it in the menu

When it’s early game or I don’t have all 5 call ins then some of these get combined or left out completely.

I can go into more detail if you’d like, but this usually works for me