When I'm in NYC, I usually go to the Madison Ave store. If I were looking for something special, I'd call my SA at Wall St and go there, but if just popping in, it's Madison for convenience.
I've been to the BH store - don't like the SA's there - they'll ignore you even if the store is totally empty. Chicago is nice (nice SA there), but they have very little stock, and I think what they do have is reserved for their regulars, not drop-ins.
I HATED Sloan St in London - SA's had never heard of half the small leather goods I wanted to see and were generally indifferent. I've had good service at Bond St but was only looking for a scarf - have no idea what it would be like looking for a handbag.
FSH is my "must" store if I am in Paris. The selection is amazing. One often must wait to be helped, but I've always found the SA's very nice and helpful if I waited patiently. It's just an amazing store. I have not been to the other store in Paris - never enough time and I found what I wanted at the FSH anyway.