Since the itineraries look the same to me, I would probably pick the Liberty. If the price was the same of course. The Triumph doesn't have the Seaside Theater yet. However, the Triumph is scheduled for drydock in late September and may just get it. Again, price would be the deciding factor for me.
Another thing, just because the cabins are on the Port Side of the ship, doesn't mean the ship will be docking that way. Just in case that was a consideration about the cabin numbers. You would have to research each ship's docking history, and even then it could change.
You are doing the right thing by booking early. Good Luck!