I think the sunset is going to be a huge morph, but it's going to be an expensive one, like the bananas.
As far as I'm concerned, the "hottest morphs" are split into 2 categories. The ones that are too expensive for the hobby breeder (such as myself), and the game changing morphs that mostly the serious investment breeders will purchase. The bananas and GHIs are those investor morphs. They're slowly reaching the hands of the hobby breeders. HGWs and Ultramels are starting to come down low enough in price for us hobby breeders to be able to afford. I think a single gene worth around 2-3k is pretty high end for a hobby breeder. 5k+ for a single gene is more of an investment animal.
I voted ultramel to be the hot 2013 morph since they've finally started to come down in price (for males at least).
GHI combos are already crazy. HGW combos are pretty sick when you add the right genes. The pastel hgw isn't anything special IMO, but adding yellowbelly or enchi turns it up a lot. Ultramel, like the hypo or caramel gene, will really shine with certain morphs, but some won't be super crazy unless you add more. Since ultramel is more of a color mutation, adding more cool colors in the mix will do ya best.
I saw someone mentioned the blackhead. Some of the blackhead combos are pretty cool, but the fact that the blackhead spider isn't spectacular really puts it lower on the hot list for me. The fact that it has a super literally doubles any combo potential that it has, so I can't say for certain what my verdict is.