I love serp for coal. I dont go there for coal specifically, but when I do go there for gems I come back with a decent chunk of medium coal and almost a stack of hard.
But for soft coal (for compacting) I do prefer Grovidias Te over Gloviasa just becuase the terrain is a bit more forgiving. I can get enough coal for a mass compact in about 10-20 minutes.
If I could compact medium coal then I’d just go to serp everytime. But alas, those nefarious rubies have been alluding me…