This is our first cruise so I write this with the caveat that we have no experience to base this on other than this cruise.
We decided to go with Royal Caribbean as they seemed to address the family market well. Not knowing if we would like cruising we chose to book with a guaranteed inside cabin.
Before you read on I want to say that we had a fantastic cruise experience and all the staff and the dining were exceptional despite the cruise being disrupted by very bad weather.
Inside Cabin along the centre line, at the bow of the ship. Not massive but ok. We had 3 people and a wheelchair. To make a bit more space we put the table in the cupboard and the suitcases under the beds.