One thing to consider is that a 7 day will most likely give you a newer, better maintained ship with more amenities. Our first cruise was a 4 day out of Long Beach on one of Carnival’s older ships. We had a good time but it wasn’t an experience I felt I needed to repeat. I did however want to take our son on a Disney cruise. At that time, 2003, they were only sailing out of Port Canaveral. No way we’re flying from Sacramento to Florida for a 3 or 4 day cruise on the Wonder. Took a 7 day on the DCL Magic and discovered I LOVED cruising! DCL isn’t my cruise line of choice any longer, I’m more a Princess or Cunard customer, but I’m thankful for that first 7 day cruise.
I always tell people to do a 7 day over 3-5…better ship, ports, activities and a much better idea of what cruising is really like.