I ran a unit of grave guard all last tournament season until the 50-50 Lords errata came into effect, where I switched to double-blender BK bus.
My feelings on the horde is that it lacks reach, and struggles against avoidance lists or lists with lots of speed. It's also very fragile, and requires a significant amount of finesse to use. The BK bus is certainly the "easier" option (funny, because I see so many more new players gravitating towards the grave guard).
After a season of running it, my impression was that Horde simply isn't the best way to do it. To make it work you need 35-40 models, and at that size the unit is too cumbersome, too expensive, and too many enemy units can fit into its frontage. And as you'll learn with VC units, their absolute bane is fighting LOTS of attacks all at once. You can passively tank a certain amount of damage with Invocation and return attacks, but too much damage and crumble will quickly overwhelm them.
Thus I preferred running them 7-wide, and using the extra points to buy a wight king with the night shroud. Not only does he protect the unit by blocking out a number of incoming GW/lance/magic weapon attacks, but he also can stand next to the VL and guarantee him ASF rerolls even against elves. He's the best utility piece in the game.
7-wide also shrinks the wide of the unit, allowing you to fit more into your march bubble. That's one of the really big issues with the GG brick...unlike the BK it really needs support from your core in order to protect its flanks and ensure good matchups. However also unlike the BK bus it crowds up that very same space dramatically. 7-wide makes it much easier to fit everything in without having them bump up against each other or chaff each other from counter-charges.