In 6b, you shouldn't have any trouble overwintering anything that is rated Zone 6 hardy or for a lower zone such as 5,4,3,2. I am a very borderline 6a and have routinely overwintered evergreens such as pine, spruce, fir, arborvitae, junipers in various sizes of containers.

I think it's mainly a matter of finding what appeals to you and will work in your situation. If they are the right profile/shape, probably something like a Skyrocket Juniper or an Emerald Green Arborvitae should overwinter with no problem.

Sharon

It is important to make sure that your containers have good drainage.
Just in case your deck is very windy, you may consider wrapping them in burlap for the winter.
What kind of containers are you using?
Rina

Zone ratings don't really apply when plants are containerized, at least not to the roots of the plant. Containers will freeze solid without protection, and it doesn't really matter what zone hardiness a plant is when it's roots are contained in a solid block of frozen potting mix. :).