The new codex contains two generic infantry HQ units, the Ethereal and the Cadre Fireblade, and three special characters, Darkstrider, Aun'Shi and Aun'Va. Compared to the Commander, these are definitely budget HQ choices, but that doesn't mean they're bad.
The Ethereal and the Fireblade are standard infantry leaders, and in that role they offer a decent return on a minimal investment. The Fireblade is LD9, with a BS5 Markerlight and Split Fire, but his real value is his Volley Fire special rule. Volley Fire allows the Fireblade's unit to fire an additional shot, with pulse rifles or carbines, provided they didn't move that turn. This makes the Fireblade excellent for joining an objective-holding squad; since they aren't going anywhere they can take full advantage of his special rule, and his strong LD will keep them from breaking when the inevitable counter-fire comes. The Fireblade can take two drones, but since he lacks a drone controller marker drones aren't much use, and being embedded in a 12-strong unit (because there's no point in fielding the Fireblade with less than a full-strength squad) means shield drones are fairly pointless. A pair of gun drones isn't a bad investment, though, since they will benefit from Volley Fire as well. Combined with a pair of gun drones from a Fire Warrior squad, and you could have seventeen models putting out 38 shots at 18", or 51 shots at 15". Even Terminators might re-think charging into that kind of Overwatch.
The Ethereal is slightly cheaper, but even more of a support model, offering a 12" bubble of both LD10 and Invocation of the Elements. This new special ability allows the Ethereal to grant units within range one of four abilities each turn; Stubborn, FNP (6+), firing Snap Shots after running, or firing an extra shot at half range. This last ability explicitly does not stack from multiple Ethereals, but there is no such restriction on using it in conjunction with a Fireblade's Volley Fire. For just twenty-five points more than a naked Commander, that's not a bad combination.
Unfortunately, for reasons beyond all comprehension the Ethereal still takes to the field bare ass naked, and as a T3 model it's not that hard to get rid of. Curiously, while the Commander's bodyguard team have a special rule that allow them to automatically pass Look Out, Sir! rolls for the Commander, Ethereals don't get something similar. These models should be kept in cover, out of sight if possible; sticking them in a Devilfish with a disruption pod that's going Flat Out isn't a bad idea. Unlike the Fireblade Ethereals do have a few options, but none that are all that impressive. They can have a blacksun filter, which isn't bad if they're planning to start the game attached to a Fire Warrior squad, or a homing beacon, which is unlikely to be useful since Ethereals will spend their time as far as possible from the enemy. They can also have either an honour blade (+2S, two-handed) or two equalizers (AP4), but given that the Ethereal has no armour and I3, neither of them are worth even the token points cost; if an Ethereal gets in a fight, it's going to die. Better to save the points for tools that can keep it out of trouble in the first place. Particularly since the Ethereal gives up an additional VP when its killed; it's not making half your army flee the table any longer, but you still don't want to lose them if you can avoid it.
Along with the generic infantry HQ units, the new codex has three special characters; the brand new Darkstrider, the returning Aun'Va, and the long-lost Aun'Shi. Darkstrider is a special Pathfinder, with the attendant lousy armour (5+), but some tempting utility. He comes with a handful of special rules, including Outflank and Scouts, and his unique rule Fighting Retreat, which allows his unit to consolidate d6" away after firing Overwatch. He's another BS5 model with a markerlight, but sadly he lacks Split Fire, and it's not networked. Most interesting, however, is his Structural Analyzer, a handy little techno-eyepatch that inflicts -1T on whatever his unit is shooting at. The modified value is used for calculating Instant Death, but sadly Darkstrider also has Fight on Foot, which restricts him to only joining units of Fire Warriors or Pathfinders and cuts off his access to most of the army's high-strength weapons. He can still make Pathfinders' rail and ion rifles damn scary for T4 models, but I think his best use is going to be leading a squad of Fire Warriors (in a Devilfish for speed, or on foot with drones for maximum shot volume) in from Outflank to blast rear area infantry units to smithereens. It's an expensive little investment, but being able to wound nearly all infantry on 2s will definitely make the saves pile up.
Aun'Va is an Ethereal on steroids; his LD10 bubble extends to all friendly Codex: Tau Empire units on the battlefield, and he can invoke two 'elements' a turn. He's also managed to grasp the concept of armour, though he's still only got a 5+ save. His Warlord trait is quite useful, a one-shot that allows you to stand back up all models that have gone to ground at the start of your movement phase. Duck down to weather an alpha strike as completely as possible, hop back up to unleash your own. He's also got a neat little signature system, the Paradox of Duality, which lets his unit ignore an unsaved wound from a shooting attack so long as you can roll equal to or over its AP value on a d6 (it automatically negates AP1, but fails against AP–). Unfortunately, in his hover-throne Aun'Va is Very Bulky, meaning you can't put him in a Devilfish for safekeeping, and since he has two Ethereal Guards he can't join a big unit of infantry for protection. The Supreme Ethereal is supremely vulnerable, and as an Ethereal Warlord gives up two VP when he goes down (three in Purge the Alien). Aun'Va is that most dreaded of things, a finesse unit, though he is at least one with some very solid benefits to offer all the time, rather than just the one in a million time you manage to use him just right.
Finally, there's Aun'Va's colleague, the long-lost Aun'Shi. Apparently he took a break to go learn something about protecting himself, since Aun'Shi comes with a shield generator, though he's as naked as a standard Ethereal otherwise. With WS5, I5, and A4, Aun'Shi is one of the two most deadly close combat models in the book, though since this is Tau that's still damning with faint praise. His special rule is Blademaster, allowing him to either re-roll his saves or have Rending, though sadly it only works in a challenge. Aun'Shi costs almost twice what a standard Ethereal does, and has only marginally better survival prospects; alone he's dead from the start, in a unit he's alive only until that unit is blasted apart at which point, well, he's alone. See point one. An unarmoured challenge character with a two-handed weapon is not a great combination. Curiously, Aun'Shi is the only special character leader (Darkstrider is explicitly not a cadre commander) who rolls on the Warlord table for his trait.
So, those are the infantry HQ choices for Tau, and they're refreshingly solid. The Fireblade and the Ethereal are excellent for smaller games, where sinking a hundred and seventy-five points into a single model might not be cost-effective, and Darkstrider and Aun'Va offer some interesting utility as support characters. The only misstep is Aun'Shi, who has been dragged out of retirement to a rather ignominious reception. He's not terrible in himself, but he's not great either, and he's relatively expensive. I'd be surprised to see the Hero of Fio'Vash take to the field with any kind of regularity.
Next, the rival suit commanders, students of Puretide and figureheads of two very different martial traditions!