Ok, I'll bite and try a stab at this.
I have this style of
Gucci bag but in the regular brown canvas with brown leather trim. It's a really classy bag and it's super useful. I carry it pretty much almost every day to work. Because the one you're looking at is silver, it'll definitely stand out just because the bag is a pretty decent size. Usually you see the metallic leathers on smaller purses. So it will be an attention grabber. I LOVE how the GG hardware at the front blends in SO well with the silver leather!
Saying that... this Gucci is definitely a LOT less flashy than the LV Miroir line. Just going by the pictures online as well as in the various November/December magazines, the Miroir line is super shiny/reflective so it's much more "in your face" than the Gucci. I'm not sure which style you're thinking of for the Miroir?
If it's a purchase that can wait, I'd go and take a look at the Miroir, carry it and see if you like it. I think this Gucci bag will be around longer than the Miroir because there's all these rumours that the Miroir is super limited so there will potentially be a frenzy when it comes out when everyone wants to get one because there's so few. Also, this style also come out in the Britt collection so it's likely that quite a few have already got this style of bag in brown or black leather already and may not shell out for the metallic leather version.
I also think your decision will depend on what your planned use is. I see this Gucci as more wearable every day if you chose to, whereas anything Miroir is really flashy so it'd be a real statement piece that you probably wouldn't use every day.
Besides the fact that the Gucci is leather and the Miroir is PVC, if you care about re-sale value, then I'm pretty sure the LV Miroir piece will keep its value better despite the fact that it's PVC.
If it were me choosing, I think I would probably end up with the Gucci just because it's more practical. I love the Miroir Speedy, but where I am currently in my life - if I'm spending a wackload of money on a bag (4 digits) then I really need to be using it a TON. So I think that would be my ultimate deciding factor... if I were able to buy bags for pure collection purposes then I would pick the miroir!