The old Heavy Support slot used to be only slightly less of a no-brainer than the old Elites slot; two squads of XV88s and a Hammerhead, with the number of the former depending on the size of the game. Enough has changed, though, that it's not always so easy to decide. And, as Martha Stewart used to say, that's a good thing.
Of all the units in the entire book, the changes to the XV88 were the most controversial. When it was first leaked that their railguns (now heavy rail rifles) were going to drop from S10 to S8, for essentially no change in points costs, I'm not too proud to admit that I worried the sky was about to fall in on the Tau. Thankfully, I can say that my fears were unfounded.
While they're not cheap on their own, clocking in at 65 points per model for BS3 and T4 with no native invulnerable save, armed primarily with heavy weapons but lacking either Relentless or Slow and Purposeful, it's rare that you won't find them pulling their weight, especially if you routinely find a flyer or two on the other side of the table. As far as options go, XV88s have some interesting ones. One of their number can be upgraded to a shas'ui, which is moderately useful for the +1LD (and not at all for the +1A), though curiously the upgrade offers no access to additional options or wargear. They can have a bonding knife, which is useless unless you're bringing at least two drones along, as a full-sized squad of XV88s can never be below 25%. More interesting, they have access to a couple of neat weapon options. First, they can swap their SMS for twin-linked plasma rifles, though given how useful a weapon that ignores LOS and cover can be, it can go either way. They can also bolt on a single seeker missile, adding in another S8 shot, albeit of the one-use-only variety. They get all the usual drone options, gun, marker and shield, but also get a missile drone, the only unit in the codex that can take the missile pod-armed death-frisbees. And finally, continuing the unit's apparent love affair with all things missile, they can trade their heavy rail rifles for a twin-linked high yield missile pod, essentially a pair of twin-linked missile pods bolted together.. There are those who like this for the shot volume, but like the Razorshark and Sunshark, Tau don't often find themselves struggling to get access to S7 firepower. The fact that they can't move and fire the 36" high yield missile pods at anything but a snap shot is also a bit of a kicker.
Along with weapons, the XV88s have some good options in the support systems list. The most well-known is, of course, the velocity tracker, making XV88s the only Skyfire-possessing ground unit with an AP1 weapon, but there are others. Combining the early warning override with the high yield missile pods and plasma rifles can give a full-sized unit a pretty good chance at downing an incoming flyer before it gets a shot off, even without Skyfire, and giving each suit a seeker missile and target lock can provide considerable tactical flexibility if you regularly find yourself facing large numbers of light vehicles or flying monstrous creatures. The rest are mostly middling options, ranging from too expensive (shield generator vs. 2 x shield drones) to too weak (most of the guns that will cut through their 2+ will ignore stimulant injectors) to too great an opportunity cost (HYMP and counterfire defence or advanced targeting systems makes for reliable damage, but at the cost of either Skyfire or Interceptor). Amusingly, XV88s are explicitly barred from taking vectored retro thrusters.
The unit did get worse against its old targets, heavy tanks and AV14, there's no question. But Tau got more tools to deal with those threats, and XV88s moved from anti-armour to anti-flyer, and did it very well indeed. Unless you routinely come up against seriously flyer-heavy armies like Necron Air (4+ Night Scythes) and Flying Circus (multiple FMCs) you probably won't find it worthwhile bringing along more than one of these units, though. They're still good, but they're not the powerhouse they once were.
If the XV88 got arguably worse, though, the Sniper Drone Team was indisputably improved in this new codex. The old unit sucked; the drones lacked Relentless because of the spotter so they couldn't move and fire their heavy weapons, the whole unit disappeared if you lost the spotter, and their weapon loadouts weren't particularly impressive. Oh, and a team of three cost as much as an XV88. While it would be hard to do anything but improve, the extent to which they did so is pretty staggering.
The first big change is their accuracy; while the drones themselves are only BS2, their firesight marksman carries a drone controller, allowing them to make use of his staggering BS5. Their weapons are no longer rail rifles, but longshot pulse rifles, 48" rapid fire sniper weapons. This makes them ideal for dealing with monstrous creatures, which are becoming increasingly common as 6th edition marches on. Stealth gives them some decent protection, and the firesight marksman comes with a markerlight, though sadly it's neither networked nor equipped with a target lock. And all this, for a 22-point price drop!
The only options the unit has is to add up to two additional marskmen and six additional drones, none of which are a bad idea. There are those who council running a full-sized drone contingent and engineering the death of the marksman, replacing him with a commander with a drone controller to give them BS5 and increased mobility (and perhaps Monster Hunter with the PENchip, too), but this isn't without its risks; without the marksman to slow them down the drones will fall back 3D6" if they break, and with just LD7 that's not unlikely if they take casualties. Really, the best use for these guys is to bring along as big of a unit as you can, both to protect against loss-induced LD tests and for maximum shot output, and pour BS5 sniper fire into anything T5 and up. No need to get fancy with them.
This section has actually turned out quite a bit longer than I expected it too; apparently, there was more to say about the Heavy Support section than I'd thought! That's a nice change from the old book, where it basically boiled down to 'take XV88s, give them ASS or targeting arrays, and bring along a railHead in case of hordes'. So, now that we've covered the infantry, next time we'll take a look at the grav tanks of the Tau Empire, and see just how fierce competition for this slot can get!
Here's a hint; pretty damn!