Vallejo acrylic metallics are somewhat fragile, becoming less so after a day or two of hardening. Take care masking to overpaint or polishing.
Alclad lacquers are rock hard pretty much right away. I have buffed them with an old T-shirt with no problems. I've masked and oversprayed with some Model Color. Be sure to hold your mouth right when unmasking, but nothing major. I've even stripped Model Air/Model Color from an Alclad surface with an overnight soak in Windex and some light brushing. The Alclad was not affected
Given the two, I'd stick with the Alclad