Lucifer's War seems like the nicest title to me. It seems like something that would have a decent story behind it compared to the other two. I tend to think narrative rather than multiplayer. The steampunk setting you've come up with would lend itself to a nice campaign I think, a bit of explanation of the differences between our world and this one.
A war over HellCoal seems like a plausible idea. It's slow-burning and can produce a lot of energy over a long time. If its a finite resource of that power people would fight over it a lot! Idea: Have Hellcoal as a finite upgrade for weapons that will increase their power and last for several shots as opposed to the normal coal which will need to be replenished constantly. In order to balance the game it would have to be a really rare occurence that you found it since it would last for a while. (V. small pieces of HellCoal perhaps that would last a max of 5 shots?)