Firstly, though, I wouldn't choose to give a Pokémon like Zekrom items like the choice band or choice scarf. Basically, it only limits the Pokémon to one move and in case you need to use another move switching it out and back in again would waste two whole turns and it's not worth it. If I were to use the choice (band, scarf, specs), I think it's more worth it to give it to a Pokémon who knows Trick so the opponent can't use a new move, although there are quite some restrictions to that.
Personally I will choose Choice Scarf (the one raises speed) because Zekrom has a really reliable attack (in fact its the strongest) stat while it's speed is the weakest, so the scarf can give it a nice boost.
