My oldest is 5405, the Victorian general and his buddy, because at some point I bought two. That duopack Graham posted is the only MIB I have without an opened double. I normally don't like blisters, but they are great for MIB. Then I have some duplicates from PCC days, and a few of the other historical exclusives.
I don't have the money and space to be a MIB collector. I couldn't store a large MIB set. Mine are all figures. As it is, I may have to re-evaluate my MIBs. Eventually.