I dry hop in an oversize bucket; same type used for primary fermentation.
If I was going to do plain extended aging, I would want a carboy or BB that was sized so that the beer would be up in the neck, so it was less exposed to oxygen. However, that's not really compatible with dry hopping because the hops take up room and it's really annoying to get the hops through the carboy neck.
Secondary for aging (no dry hops): Carboy
Dry hopping: Bucket