Familyof4

If your looking to just a little later that traditional early dining them go with MTD and pre-book your times for 6:30-6:45PM.  When we have done this they have always sat us at the same table with the same wait staff.  The only thing is if you like to sit at big table with the same tablemates every evening then go traditional.
 
Edited to add:  If you tell the wait staff you are trying to get out at a specific time for a show they will usually do their best to accommodate you.

Adventure is a great ship for your first cruise. You are going to love it !
 
Unfortunately, the show times are not published b/c they are so fluid and always subject to change. As a rule, there will be an early show - generally around 8:00 PM and a late show, generally around 10 PM...but each ship maintains its own schedule for such things.
 
If you are planning on going to the evening shows, I would recommend that you choose another dining time other than 8:30. That is going to be right smack dab in the middle of the 2 show cycles and will likely make getting to the shows a little problematic.
 
Personally, I always eat as early as possible so that I can get that out of the way...but that's just me.

I'm a big fan of MTD - I like being able to go to dining when I want and often meet people on the cruise
that I like to eat with.  I still do traditional if we go with a few family groups but overall we like MTD
And I do pre-book for dining times a lot before we get on the ship with MTD just so I have
something, but the wait staff does very well trying to accommodate changes once on the ship too
With Teens I would think MTD would be better than 830 since they may have things going on
at night, and will not want to be sitting at dinner until about 10pm, just my thoughts