The really large ones like EPD, KMP and ETP are pretty much all the above now. Each has their own concentrations but only EPD was first to focus on liquids. Beating even Mr. Kinder on that one.
PAA is also branching out but they do more delivery of finished products.
So perhaps today it is more a matter of whether it is a large foot print diversified pipe or a more regional pipe defined by the resource developed in their locality.
EPT has some long haul natural gas pipes up into New England which no longer have a reason to exist. However, they are converting those pipes to oil or liquids now. They are also trying to do the same with a gas line in the MW no one needs. So right of ways while difficult to value are important.