I definitely suggest purchasing at Barneys. I'm a loyal Bergdorf's customer and love shopping there. The customer experience is usually great but Barneys wins in this case! The reason I prefer buying Goyard at Barneys is because Barneys is the store that brought Goyard to the states. Goyard was trying to choose between having their bags and luggage sold at Barneys or Bergdorf's. Goyard decided on Barneys and that's why I buy their products at Barneys. It wasn't till a few years later that Bergdorf's began carrying Goyard. Just in case you want another bit of Goyard's history, it was established before Louis Vuitton. In fact, Louis Vuitton worked for and was trained at Goyard. For this reason, I choose Goyard over Louis Vuitton any day (plus it's more exclusive!).
Phyllis @ Bergdorf is super duper nice: she responds to email promptly, answered all my questions patiently and thoroughly (I did ask a lot) and on top of that, she sent a few pictures of the bag in stock since I was undecided on which bags and what colors. Very friendly and she'll give you honest opinion if you ask for her advice.
I purchase at both Bergdorf's and Barneys, just depends on where I am that day. Also it completely depends on what I'm looking for and who has what in stock. Bergdorf's seems to have a better variety of the smaller items.
I work with the same woman at Bergdorfs all the time and she's very knowledgeable about the product. At Barneys everytime I go there's someone different there. I have found them to be not as knowledgeable or forthcoming with info but that really doesn't matter because I always know what I'm looking for.
One woman I worked with at Barneys was wonderful and the other girls I could take or leave.