Voted for Ghost / Fire, but Ghost / Fighting and Ghost / Water are interesting. Its just that there have been lots of exotic Fighting pogies created in the last two gen, such as Lucario, Toxicroak, Gallade, Medicham, Breloom, and Infernape, and the only notorious Fire inventions were Fire / Fighting and Fire / Steel (alright there's the cool Camerupt, too). The promise of Ghost / Fighting that futuresuperstar has so elaborately explained is very appealing, though. Being able to take any hit that Heracross dishes out is very cool, as long as this Ghost doesn't have Gengar's Defense. I have to say, however, that TTar's Crunch is neutral, so it's not quite a counter for Ttar, and its resistance to SR is nothing special, since its a Fighting Type after all. I admit that the priority move bit was interesting (bullet punch and shadow sneak still hits neutral and SE, respectively, unfortunately).
There are tons of water Pokemon already, but Ghost / Waterseems really cool and competitive. Normal / Ghost is kind of bleh imo, and I can't help but imagine an alter-ego of Bronzong for Ghost / Steel, despite having no Levitate! Ghost / Psychic interests me, but I'm getting sick of all the Psychics we already have. Grass (Gravy lol!) had some nice upgrades this gen I think, I don't see Ghost / Grass being any more unique than the other defensive and offensive grasses we already got anyways.
As for Fire's illustration, I believe there are a lot of promise, and people could be pretty creative about this rather than going with something predictable. Something pokemonish could definitely come out from it. I don't like the oni-mask idea, sorry =p.