Hi bannYlein,
I am usually at Prada/Miu Miu subforum (love Prada bags!) and I have a coffer myself which I also love... but between the two, I would pick the Halo. It is limited edition, unlike the coffer which is a staple design of Miu Miu, which you can buy later. Plus the silver will match more outfits than zaffiro.
Halo is much smaller, though.. will it fit your needs?
P.S. I'm looking into getting a halo too!
P.P.S. Be sure you get your hands on a coffer, though. That bag is definitely worth owning and is one of my faves!