For the first timer it can be difficult to raise Great whites, or BB bronze just starting out. They can be really difficult to get started unless your read up on the best practices for them. Also even if you butcher earily you could have a 20 to 25 lb or larger turkey. Which is getting close to the upper limit for using normal cooking equipment.
Last years thanksgiving turkey we had a Blue slate we butchered (28 weeks) slightly earily, that came in about 12 lbs. More then enough meat for a family of 4, with left overs.
So the first question is, how many do you want to feed, and how much left overs? A 18 lb turkey will easily feed 6 adults.
If you are feeding 6 or so adults and teens a larger hearitage would work nicely.
We had all of our turkeys on grass last year and the Red Bourbon and Blue slate tasted so much better then the Great white and BB bronze in our opinion. Except when we smoked the meat, then they were about the same.
But Red Bourbon's tend to forage more, and wander further when we free ranged them.
Tom