I picked Grom'Gol in STV but.. You must think about the mobs around the base. The number and level of the mobs will certainly limit the range of levels that are able to go on the Raid. I would have voted or Sepulcher in the Silverpine Forest if it was an option. There are almost no higher level mobs there- even though the mobs around Grom'Gol in STV are in the 30's, they still aggro you 60's and when you have guards pounding on you it isnt a good idea to have extra damage being done.
~Tarren Mill is raided entirely too much.
~Hammerfall has higher level mobs aorund it too, but not as close as Grom'Gol.
~The Crossroads in the Barrens is too much of a hub for the Horde. Everyone and their brother will be there as soon as we land =\.
~Splintertree Post wasnt that fun last time lol.
~Camp Mojache is too high for most of the guild to go.
~ The Undercity.... are you crazy...
Another good place would be The Horde landing place in Desolace, Shadowprey Village. There are only 2 ways for horde to enter: walk in along the beach or fly in. Thats a nice place to raid and once we get there, there will be little higher level mobs for the lowbies to get killed by.