We are cruise newbies (i have never been on one) plus suffer from a little claustrophobia was the main factor in wanting a 4 or 5. I need to feel as open as I can (as silly as that sounds). Windows / patios are a must to keep me from freaking out.
We've been in both Cat 4 and Cat 5. There's really no difference, as far as feeling closed in. Cat 6 is exactly the same as Cat 5, but on a lower deck.
The verandah is great. You can always sit out there while your little one is taking a nap (as long as the sun isn't too hot.)
Kathy