I like the two bag setup better because then you can actually "place" the weight better and not have as much sloshing if you don't fill them all the way.
This is, of course, coming from a skier that has been kicking the ballast idea around for my boarding friends that seem to get bored behind my ride. (his older supra is like a brick to ski behind but decent for boarding with just people in it)
Does anyone use a household current pump (115/230V) to fill their ballast? We have a sprinkler pump that pumps out of the lake that is like 60 gpm, that should fill them in a jiffy - and it is about 20 feet from the epic's lift.