I have the ubiquitous Dwarf Colorado Blue Spruce in 5 of my containers. They all get through the winter. My boxwoods don't look too good that I put in containers last year. They looked good until the spring. I didn't think it would make it, they're only hardy to zone 5, I believe, and you should only put plants in pots that are hardy to two zones below yours. Sometimes one zone below is okay to. So I would look for plants at zone 3 to put in pots to get through the winter. Type of container depends on your taste and budget. Just make sure drainage is good and it won't crack during all our freezes and thaws. Terra cotta will crack, so that's out.

I'm in northern Indiana...just east of Chicagoland. I had 2 boxwoods--Green Gem--in fiberglass pots (with drainage holes) on my front steps. They over wintered fine the first year, but not the 2nd. Not sure why since last winter wasn't overly horrible. But maybe the really cold weather in December did them in. I gave up and put annuals in the pots for this summer. I'm thinking I might do willowtwigs & berries for the fall/winter. I really liked the boxwoods though...