kfly, If the itin is a very high priority I'd consider HAL with teens. If there is another more children friendly sailing similar I'd consider that strongly. HAL has facilities and there will indeed be families onboard during the holidays. HAL has a reputation as among the most senior of cruiselines. It's not the staff, other families or facilities I'd be concerned about. Its the loyal passengers. There is an expectation by many frequent passengers that there be quiet early. Since HAL markets to seniors and gears entertainment and other things toward their primary clientelle, it may just not be what the teenagers have in mind for vacation.
Some good options to look for among mainstream lines would be RCCL, Carnival, NCL's newer ships (Pearl and Gem would be the best fit) and even Princess. Princess, although not known so much as a family cruiseline does a very good job with families and are moving more in that direction recently.
Not that HAL would be a bad experience, just not probably the best choice for the teens.