Looking to buy in bulk to feed 50 people
The only kind of short ribs I grill are korean style, or flanken. They are cut very thin across the bones so they do not have to cook a long time. Otherwise I slow cook short ribs (with or without bone) because they take a long time to cook.
Yes, flanken is the preferred cut (in Korea Town called "LA Cut"). But Steve Raichlen has interesting trick for opening up the short fat ones. You make a series of cuts to unfold the meat from the bone but still leaving the bone end attached. It's diagramed in his "Barbecue Bible" but I think he also has a video demo out there. Either Google or Bing his name and you may get lucky.
I'd definitely buy them cut lengthwise as flanken (or Korean bbq style.) Much easier than butchering enough short fat ones to grill for 50 people - and at least around here, the cost is the same.
If you go Korean style have a bunch of scissors on hand so that you and/or your guests can cut through the meat between the bone sections on the flanken cut. The idea is that you pick up the bone end with your finger tips and munch (although you can use a knife and fork).