I'd go with rogue. Rogue has always been good. Even when they are not individually strong, as long as a class they pair well with is strong, then they also become strong. Examples would be rogue mage. The CC the 2 classes can rotate out in a synergized setup is just insane. Always has been, always will be.
Rogue is pretty strong now also. The assassination nerfs seem fairly minimal, and they still pull A LOT of damage. With rogue's current design, I just don't see them being bad, let alone unviable at any point soon. The specs offer a lot between themselves.
Warlocks have been good almost throughout all of wow, however, they have had their ups and downs. And unlike what rogues have to offer, if warlocks get nerfed to a bad spot, then that's that. They'll be bad. They simply don't offer the same a rogue does (obviously, but still needed to be said). However, Demonology seems incredibly strong at the moment. LSD with demo enhance rdruid is insane right now.
TLDR; I prefer rogue. Both classes are strong atm.