I find myself only using up to 10 of them on a certain base, I'm not sure why everyone is talking about dropping 30+ raiders on a base, even if it has good loot, it's good to target those bases which have their resources exposed. This is much easier if you're medal dropping, though, and it's the best, albeit the most boring, way to loot. Typically, bases which have the Pyramids are the best for this, as it's silly to keep farms and wonders in walls (unless it's FC, etc.,). Those players, provided they've been off for a while and/or haven't collected in a bit, are always the best for raids.
Regardless, I think that they need to have priorities. I don't need some house with 60 food and gold destroyed, I need the mill with 110k, or the farm(s) with 25k each taken out, before the raiders get swarmed by horsemen and foot soldiers.