For CORs who have both DP and Earp: When do you find yourself using one over the other?
Are you using Leaden? DP.
Are you doing anything besides Leaden? Prime.
If you add in TP Gun and Empy gun to the mix it becomes a little different though. Obviously Empy Gun is for Wildfire. You might think DP is good for Dynamis W1-2, but it's not. You can one-shot statues with TP Gun, which is what you should be using so you can do Savage Blades on the enemies when the statues are all dead. You should use Prime/Fomal on Wave 3 because you can do 99k Hotshots with them.
It's still worth putting on DP for the Wave 1 boss though, about 5-6 good skillchains where you close darkness with Leaden DP will kill it. But you can also just Leaden in any other gun and still kill it in 7 or 8 SC instead and it wouldn't matter much.