Between the Gabby and the vanity case, my personal preference would be the Gabby. I may be wrong, but I think Gabby has more chances at staying than the vanity case. Chanel has already released a standard version, the iridescent reinbow hardware version, and the cheveron version. The only one remaining is the all black hardware version, which I think will be released soon. I actually think that, at lease for now, small black Gabby is not very easy to find pre-loved. I was not really looking very hard, but within the past two or three months I have not seen a single black small Gabby on
Fashionphile, which leads me to believe that they are eather sold very quickly or are not sold pre-loved in large quantities, making them pretty hot item on the pre-loved market.
I agree with Stylistbydesign that vanity case-like design bags are not very user friendly. I do not favor the Chanel version, but I have the small Valentino version with two zippers, and the square shape makes it very impractical to open and close. For that reason I do not really reach for it often.