Well...Khali is already a World Champion. I wouldn't say he'll be gone for a while. That's more than enough reason.
CM Punk and Lashley are bad choices, no offense. They're both good wrestlers, Lashley just needs some tune up on the mic and spots. CM Punk is young as well as Lashley, and the only direction they can go is up.
As for Marella, I really don't know what to think of him. He's just so damn bad, doesn't have a finisher, can't talk well, can't wrestle well - he's worthless. But he is also young, so he might just get sent back to OVW and come back again. I couldn't really say yet what's going to become of him. Everyone is right, that he's already getting heat. Maybe this was the plan, if he can't get over as a face, make him look like an idiot and become heel.
Snitsky is the obvious choice. He's been around for quite a while, dating back to Kane and Lita, maybe earlier, but I can't remember him anywhere before that. And what does he have to show for it? Err...nothing. He's going nowhere, he has no reaction, they're trying to make him a monster and the crowd just sits there and does nothing. He's not taking part in anything but squashes, which could have something to do with it. It will take some actual wrestlers and actual feuds first before I can judge.
At the moment however it's Snitsky. Unless it's different with actual wrestlers, he's history.