Visa Signature concierge is very meh in comparison to the amex platinum from my experience. (I've not used a centurion concierge, though reportedly it's the same service - I find it hard to believe that they're treated with the same service level considering the requirements and fees to be eligible for a centurion card, however)

The Amex concierge team has been able to find me items at local stores when I needed things ASAP that I was having trouble finding, and also managed to snag me a limited release item that was only available at the companies' location. (That was expensive, but still less than I saw them for being resold for online. I imagine a courier service could have been used if I was familiar with any in the area, since it was basically a 'drive there, pick up, drive to UPS store, ship' type request)