Samsung isn't going to make any changes to the manufacturing process. It wouldn't be cost effective for them. So a new one won't be any different from an old one in terms of hardware.
Now, that's not to say there won't be other differences. For instance, a newer one will likely have updated software, though it's pretty easy to update it yourself, and there will still be OTA updates for you.
The biggest advantage to a recently manufactured unit is really warranty related. If you ever lose your receipt, Samsung will not honor their warranty if the phone was manufactured over a year ago. If it's a recently manufactured phone, they generally don't bother asking for a receipt.
