Well I'll admit it, I never played all the way through Gold/Silver, in fact I only ever played right through Red/Blue/Yellow and Fire Red/ Leaf Green.
Because FR/LG are essentially R/B with new graphics I'll hold it out of my answer.
Red/Blue/Yellow are the pinnacle of the series, Gold/Silver just didn't have the same magic as the originals.
Red/Blue, had the best map design, the graphics weren't the greatest, but that was simply because of the hardware, the best monster design, it was unique, the Legendaries felt unique, powerful and RARE.
Not to mention that I'm probably one of the few, but I hate the Night/Day clock, nothing was more annoying than trying to catch a day pokemon only for it to swap to night.
I wanna play R/B/Y again now(I only ever played through on Red, as I was never addicted, just played it for fun).
Also, the new monsters are just ugly.