You'll love the Constellation. We did a pre X-mas cruise last year (debarkation 12/24), and REALLY enjoyed it. It was me, my wife and our two daughters (8, 9 at the time).
Great ship. As Tom said, some "quirks" like any ship, but great all around. We did the family view stateroom, which are the balconies off the back of the ship. Great cabin for a family.
If you're going with a smaller group, I'd still opt for a balcony. I don't think Concierge Class is necessary... frankly, I don't find the "perks" worth the additional money. The non-Concierge class cabins are the same size and just as nice.