I have just have recently sold some of my old gold, so I am familiar. This was about 3 weeks ago.
There is no set rule because when you want to to sell. I went to 6 different places. A couple of the places were "We Buy Gold" and the others were jewlery stores. In each store I had the same gold weight, but had gotten different offers from each one of the places I went to.
The best deal I had gotten was from a Jewler who does not specialize in buying gold, but does repair and sells jewlery.
I do not feel there is a set place that will give you the best amount. My best suggestion is to stay away from the "We Buy Gold". I found they offered the the least amount for the goldand in one case told me I had less than it had been weighed out at.
I suggest shopping it around. If you have a smart phone look up the exact price when you go in to each store (becasue prices change rapidly throughout the day) Have the gold weighed out so you know what you have in weight.
Your best deal most likely will come from a Jewelry Store. Shopping it around I have found is the best way to get the most money for the gold.
If you go in armed with knowledge, you can also negotiate for the best price for the gold.