In a Trooper-heavy list, if you had to choose between Grenadier and Covering Fire, which command card would you choose and why?

Covering Fire has generally been pretty bad, because the troopers you want to play, eStorms, don't really have the extra surge to spend. It's also very hard to justify over bringing 3 points worth of other really good cards.

Rebel troopers can utilize it, but they're kind of meh to begin with, only really good when focused.
Maybe Jet Troopers can utilize it some now if they're getting those 3 die attacks? Still don't know if it's really worth it.
Dewbacks? Well, you aren't getting a bunch of attacks, so it's hard to say it's worth playing.

Grenadier is still very strong, but sometimes hard to justify when facing fewer figures with higher health. There is something to be said about Grenadier and Overrun both putting on a decent amount of unblockable damage.

I recently had the idea to combine Cavalry Charge with Covering Fire. Seems legit, 7 damage Stormtroopers.

Bombs away with grenadier. I love throwing them into a crowd! Of plastic of course

I think it depends on the list. Stormtrooper equivalent is only going to have 1 surge sometimes 2 but rarely and usually there's a lot of evade floating around, so even one is iffy. Rebel troopers however tend to average 2.5 so they tend to get more mileage out of it. e Jet trooper is somewhere in the middle, if he's shooting flyby he may get more out of it and the dewbacks probably could use it but since they are a single deployment (instead of 3) there is some limit to it. On average, Grenadier is unmitigated damage so it gets an edge, but I could see some lists that would benefit from Covering Fire as well. The problem is that there is only ever room for 1-2 3pt cards (New Orders competes as well) in your deck so usually its easier to go with what is better on average or in the most likely situations as opposed to trying to line up a Covering Fire on a figure that needs extra damage and needs extra surges, and have your guys where they can get shots in, etc.

My big issue w/ Covering Fire is that if you don't have most/all of your Troopers on the board, it's pretty much worthless. You'll either have to draw it in your initial 3 cards or at the end of round 1 for it to be useful.

Closest to become viable when used with Troopers that tend to have an excess of surges, such as the Jet Trooper. It can be very much a case of hit and miss, though if it hits it can cripple certain enemy lists, particularly those dependent on melee damage (range too, if you do hit and runs dodging out of line of sight after attacking - like the Jets tend to do).