Well pick one.
Though ship "war" is probably an exaggeration. There's not really a conflict big enough to be considered a war. The problem with NaLu is that Natsu is too dense to see that Lucy has a thing for him, and Lucy is too shy to actually make a move except when she's drunk. The problem with GrayLu is that Lucy likes Natsu more than Gray, Gray likes Juvia more than Lucy, and Hiro Mashima likes NaLu more than GrayLu.
hahahaha said it jokingly, I'm NaLu Shipper to die ... but my favorite crack pairing is GrayLu xD.
In order not to do Spam, their love intentions are obvious, with Gray we had to wait until the 100-year mission to know his true feelings, Lucy is very noticeable and Natsu ... is still Natsu xD, being affectionate with Lucy to its way.
But yes, I consider that there is a good amount of GrayLu fans, even Hiro Mashima himself mentioned it at some point, so it is interesting that he does something like that, the fandom explodes xD