I prefer to use the Enforcer Troopers (PA's Army Troopers) as defensive units, they have more health than stormies and since they're on defense firing on the move doesn't really matter much.
Having said that, I'm yet to play as Zsinj or the Pentastar Alignment in 2.2, and they have AT-TEs now instead of AT-ATs, which means no free infantry. So I guess that changes things a bit for these two factions. I'd go for Stormtroopers over Army Troopers then. However, Zsinj has Raptor Troops, and PA has Storm Commandos and stuff, so there are different choices to make. All of them have their strengths and weaknesses, I'd assume.
PA does not have Storm Commandos.