I am wondering if anyone has tried both of these tomatoes and can speak to their flavor and differences? They both seem to be highly regarded.

I have not tried Apricot Brandywine, but I grow Aunt Gertie's Gold every few years and think it is one of the best orange/gold tomatoes with a nice depth of complex flavor. My impression is that Apricot Brandywine is possibly more mid-season, while Gertie is on the later side. According to Tania's database, AB's origins are somewhat murky, possibly coming over from England in the 2000's or maybe a renamed Yellow Brandywine. It would be fun to grow all three to compare.