I'd go for the Caravela,especially if you're going clone -- the one on fasttech is one of the better things they sell (along with their astro, etc.) It's a really, really well made all-around mod.
I'd avoid the 4nine. It has a few neat design features, but it's a hybrid connector and unless you know what you're doing (and even if you do) it's one of the surest ways to short your battery there is. It's just not the mech to get until you have a lot of experience under your belt, and even then I know experienced vapers who'd never shorted a battery till the 4nine (yes, their atomizers had longer positive posts).