That's a hard question to answer for two reasons. First, US 29s haven't gotten games since Cataclysm, and while interest is rebuilding, we really don't know how all the changes will play out on the field. EU 29s may have more insight. But second, and more importantly, your survivability as a healer really depends on your playstyle. Even at 29, you see major differences in how effective healers leverage their classes.
Resto druids do really well by staying mobile, hard to catch. That's not directly resilient, but staying out of reach of damage counts for a lot. Holy Paladins can belt out a lot of heals while under duress, thanks to their armor, and they have other abilities to help keep them afloat when they get caught up in the tide of battle. Discipline priests maintain their mobility, using bubbles and HoTs while running around, but can also deliver strong heals in clutch moments. Finally, resto shamans work partway between priests and paladins, so to speak. Resto shamans rely on a lot of damage mitigation -- intercepting, resisting, and stopping things before they start. Plus, they have decently strong heals when the time comes to defend teammates.
To answer your question and ask another, all four healing classes do well in terms of survivability. Are there particular playstyles you prefer or shy away from? That may help narrow your decision.
