Container vs. B/B is an age-old argument... It's kind of like Mac vs. PC... Each has their own set of pros and cons. Hopefully this will be a useful guide in choosing the appropriate type for your project... I'm going to assume everyone knows the general difference between the two; container trees are raised in buckets, bags or boxes their whole life and B/B trees are raised in the ground, in a field their whole life. Simple...
B/B trees are less expensive than container trees in the more commonly used sizes:
The X axis represents caliper inch, the Y axis (hidden) represents average price. The green line is B/B trees, and the purple is container. B/Bs are significantly less expensive from around 4" to 8". Prior to 4" the difference can be minimal depending on species.
B/B trees can be harvested anywhere, which can make them harder to find but still available. If you know the right digger, they can get them for you. Container trees exist only under specific conditions within a tree farm.
As expressed in my last post, when the look is a big factor, it is important to consider both options. B/Bs can be harvested anywhere as I've said, therefore just about anything you can imagine is out there... if you can find it. And don't think that digging out of your neighbor's yard isn't an option. It is. I've seen it done.
Container trees are the creme de la creme. They have been above ground in limited quantities allowing the owners to dedicate their full and undivided attention to their look. Expect big full heads, perfectly matching trees all in a nice straight line. Container trees are ideal for streetscapes and other very formal applications.
Containers have a lower mortality rate than B/Bs, it's a fact. Their entire root system is fully contained within their bucket or box so when they are planted, the roots just take off into the ground. HOWEVER, container trees are used to being watered regularly, and fertilized regularly. If these conditions do not continue after planting, the tree will not maintain its look. Also, container trees are grown in special soil which is not native to anywhere. The soil drains quick, which means they dry out quick. Consistent watering is an absolute MUST with container trees or they will die, quickly.
Assuming B/B trees are dug during the proper time, the cooler months, their biggest and only risk is in how they are handled. The rootball is bare and exposed protected only by a wire basket and a few layers of burlap. Rough handling can loosen the rootball which almost always results in failure. Since these trees are existing in Native soil, they retain water much better. This also makes B/Bs extremely heavy trees requiring heavy equipment to move. When first planted, as with anything they require regular watering but can be weaned off quicker than a container tree. During the first year after planting a B/B tree will spend 90% of its energy trying to reestablish its root system. This means, a B/B tree will put on almost 0 top growth until after its first year.
There is no right or wrong between the two choices. It's a matter of application. Consider the following elements of your project before designing in no particular order; budget, desired look, season of planting, equipment available (or accessibility of equipment), locality of your source to reduce transportation time, soil type and dedication of owner/maintenance staff to regular watering.
I hope this helps and I encourage further questions!!