Really depends on team composition, type of enemies, how the spawns both spread and are stacked, the map, levels and a bunch of other little things. Herding is not always the best, although I'd say at lower level it may be more often. Once youre in late 30s to 50s with a good team composition, you can wipe a group in the amount of time it takes a tank/brute to get aggro and pull around a corner. Especially on larger maps without a lot of spots to break line of sight.
So it's really iffy that herding will be the best, or even safest. I don't find that to be true very often at all, especially as you approach higher levels.