I prefer loam.
There are a couple of reasons that packed/blue groove are prefered by track owners though.
#1 Economy, not yours, theirs. A grooved track doesn't require as much upkeep and it does eat tires, which they hope to sell you
#2 Consistency, when a track grooves it stays more consistent from round to round compared to a looser track where it could be anything from tacky and perfect to dry and dusty. Most prefer grooved tracks for big events for this reason.