I have been tinkering with some ideas about the Haradrim of late, and it seems like they have a selection of units that is rather maddening. Not in the sense that they are unworkable, but rather, that they seem to have some obvious choices and some terrible choices.
For now, I'll constrain this set of posts to the units specifically from the tribes of Harad, and I will hit things like the Mahud, the Corsairs, Khand, and the Easterlings later. Likewise, I'm not yet going to touch on characters or monsters (keep it in your pants, you Mumak lovers).
For now, the basic Hardrim...
On the surface, the typical Harad infantry are terrible by any objective measure:
They are F3, S3, D4 for the same cost as warriors of minas tirith. They just are no match for them in combat, even with the added advantage of poisoned weapons. The numbers look like this against the WoMT:
Harad can expect to inflict 1.56 casualties per company (8 * 1/6 + 8 * 1/6 * 1/6) against the WoMT. (For the non math-savvy, that is 8 attacks with a 1/6 chance to wound, and then 1/6 of 8 attacks (as you re-roll the ones) times your 1/6 chance to wound again, which is a good enough approximation for our purposes).
The WoMT will return with 2.67 casualties (8 * 1/3), which is significantly better than the haradrim. Given that both formations are the same cost, it's pretty clear which one is better without introducing additional enhancements.
They fare even worse against cavalry, dwarves, and the like (the low defense just gets them killed in droves, and unlike orcs or goblins, they aren't cheap enough to want that to happen). So the basc haradrim, in large numbers, are just not effective without some serious buffs from Ringwraiths or the like.
Similarly, it's not like they have other characteristics that make them better - they maneuver in the same fashion, have roughly the same command options (minus the ability to take a Hasharin, which is now probably a liability more than anything else with the FAQ that ES works in duels, as he's going to get smoked by most heroes and take half his unit with him, or a taskmaster, which is of dubious use to such a poor unit to begin with), and no real other attributes to distinguish themselves. In short, I see them as inferior in all ways to WoMT, Morannon Orcs, or Easterlings, which are the comparable mannish units (one of which is a common in the same list).
Conversely, their archers are surprisingly good:
Compared to Rangers of Gondor, they are actually a decent buy. Shooting at the rangers, they will do 1.56 casualties again (same math as above), and will take 1.5 hits back in return. So here, they are actually coming out slightly ahead. More so, as defense values rise, the re-roll on the 1 becomes more valuable to the haradrim in any situation where you might be rolling twice, as your chances of having ones show up increase. Thus, while the harad infantry score pretty poorly, they outshoot rangers (and warriors of minas tirith with bows), and I don't think taking them as archers is an incredibly poor use of points. Yes, arbalesters are better, but arbalesters are criminally undercosted and not a common choice, so there is at least a rationale for taking the harad archers from a competitive standpoint.
In the case of archers, I also rarely see them taken in large blocks or with extensive command (outside of the GW battle reports, which typically include some pretty baffling army selection choices). Thus, I'd definitely consider these guys for my basic troops.
The takeaway here is this - you could take the basic warriors as an escort for a Ringwraith, most likely Khamul, with the idea that they die in droves but serve as ablative armor. Bouncing back hits against them from Khamul makes their fragility a strength; in any other case, what you are doing with them (if you take the Betrayer or Knight of Umbar, say) could probably be done better with Easterlings. Thus, if I take the basic guys, it will be with Khamul to rebound a ton of hits dealt to a large formation, and then for Khamul to leave them to die when they are crippled.
Conversely, small units of the archers are going to be superior shooting units from a common slot, and might well have a place in a solid Fallen Realms army.