Another vote for three. Yes, eating, etc. is tricky with a lap baby in any class.
As far as we know on this board, no airline bans babies from premium cabins. The airlines ban their own employees from flying with their children under certain ages (and it's like 8 or 10) from those classes. So the baby screaming in your ear is that of a paying customer.
I always recommend sitting towards the back and avoiding upper decks. If the baby cries, you can walk back to economy if the aisles are clear, or just take a walk back there to calm the baby. It's also is usually near the lavs so you don't have to walk past all your fellow passengers on the way to do a diaper change.