ARLP is 100% coal, but PVR has a large (and growing) nat gas processing operation.
ARLP has far greater coverage for its distribution than PVR does.
While ARLP's yield is much lower than PVR's, it is growing much faster (and AHGP is growing its distribution even faster). PVR just raised its distribution by a penny in the last 2 Qs. Before that, PVR's distribution had been flat at 47 cents/Q since 2008. ARLP has raised its distribution 30% since 2008.
PVR's coal ops are royalty interests, and its royalties grow with the rise in coal prices, but not immediately in most cases - its contracts call for periodic price changes, but not on a daily basis. ARLP owns and operates its mines and has benefitted more from this year's strength in coal prices. This works both ways, and ARLP has dropped more than PVR with the most recent weakness in coal prices.
I own both, BTW. And you might look at NRP as well, another coal royalty MLP which I don't like much at present.