I think all the legendary legions are fine. They each have their ups and downs.
Ithilien is good. It's like the old grey company ranger spam lists, but with the option for some d7 line troops and only a limited number of rangers that don't count towards the bow limit. How good it is will depend on the terrain and scenario; it's going to struggle with something like contest of champions. Faramir just doesn't stack up to a lot of the big names.
Grey company is basically the rangers list with some extra named hero options and only armoured RoTN. Free Anduril is all you really get from it, but it comes at the cost of no horses, no cheaper Dunedain, and no single model warbands to game the deployment when you can. It's not unplayable competitively or anything, but it's not going to be any more competitive than the current rangers list in a typical event (though it may be better at lower points levels due to the cheaper Aragorn w/ anduril).
Return of the King is basically dead of Dunharrow + aragorn with free anduril and no option for horse, armour, or a bow. Aragorn counting as a banner with free anduril is fantastic, but it's hard to compete with bringing Elessar on horse for the d7 and mount into a regular DoD force. Depends on the points value of the game though; at lower points, it will certainly be better, because you can get more bodies in. At higher points, it might not be as good, because you can pay some points for a better Aragorn, and having your heroes mounted is such a big deal.
Men of the West has no cavalry, but you can take mixed WoMT/KoDA warbands (for F4 and/or some D7) and have army-wide banner effects with Imrahil and Aragorn, and the entire army is fearless. The limited options are a balancing factor for how strong army-wide fearless and +1 Fv for a turn can be.
Army of Gothmog is fine; probably about as good as regular mordor w/ Gothmog and orc spam. It's hard to make a case for it being any better or worse overall; it's certainly better in some ways, but the lack of ringwraiths/fellbeasts matters.
The grand army of the south is good. It's the best list if you want to bring a Mumak because of the bonuses it confers to them; it also requires one. That said, Mumaks haven't been particularly competitive in the past, so it makes sense to give them a bump.
The black gate opens is good. Excellent army bonus, but limited options. You don't want to break, and you don't want to be up against armies with terror and harbinger of evil.
Cave Dragon wrote:
I wish the Haradrim War Leader had the ability to get the same upgrades as a Mumak.
It gets some of the best ones at a discount on top of the other special rules.