All of this advice is great, and Tim's response is right on target. You are likely to have a quality experience on any of these lines, but your own personal preferences will dictate where you'd feel the most comfortable. The ambience, your fellow cruisemates, your dining options, etc., really affect the experience.
Using Tim's overview, see which lines sound appealing to you and do a little more research. You'd probably be very happy with Celebrity, but you might be happier with someone else.
Let us know what you decide!