I would tell them to cruise Carnival. For a first time cruiser, the cost is low and the food and entertainment is very good. Carnival ships have a wow factor too, which new cruisers will be fascinated with and a great childrens program for family vacations. The low cost is a great factor because many people have reservations about "Being at Sea" and lets face it, cruising isn't for everyone.
IMHO.....Carnival is a great jumping off point to then move on to other cruise lines that have better dining and entertainment options.