Lots of people have their own ways of doing it, so you probably will get a lot of differing answers to this.
I use the following:
Infantry
Reg Infantry: 7xInf, 2xArt + Support (8xInf 2xArt for Offensive FM)
Heavy Infantry: 14xInf, 4xArt + Support (16xInf 4xArt for Offensive FM)
Garrison Infantry: 5xInf, 1xArt, perhaps 1xAT + moderate support
Cavalry:
Suppression Cav: 5xCav, 1xMP support
Armor:
6xArmor, 4xMot (sometimes use 3xArmor to lighten tank drain)
Motorized: 7xMot, 2xSPA or 14xMot 4xSPA
Most of these fall at 0/40 width. The 20 width units I use a lot for spreading out fast after a breakthrough, or encirclements (same number of men, 2x the province coverage). The 22 and 44 width units are only for FM who have earned the Offensive Bonus trait, which gives them a 10% bonus on width. You need to have a special layout and production run for these.