Fire Warriors
In 5th edition there were many who really didn't feel the love for these guys. The vast majority of competitive Tau players (if there was such a thing) favoured Kroot over Fire Warriors. I was pretty much in the minority with my love of these guys and dislike of Kroot. With the advent of 6th edition they were improved thanks to two main factors, the changes to Rapid Fire and the ability to glance vehicles to death. Well the new codex has only added to those improvements.
The humble fire warrior is now a measly 9pts. Pretty expensive compared to a guardsman's 5pts but you're getting a 4+ save and an S5 weapon instead of 5+ and S3. Speaking of the weapons the carbine is now two shots but I still prefer the rifle as, when using the Ethereal's bonus, you're getting 3 shots at 15" rather than 9", pretty key for Supporting Fire.
In the old codex I often ran my warriors with Photon Grenades and in the new book these are included in the cost. They are bit of a double edged sword for Tau though. On the one hand they help protect them in combat where they really struggle. On the other though they can often keep enemy units in combat for a second phase allowing them to come out in their own turn. In practise this doesn't happen all that often but it's something to think about. Tau for the most part want to be shooting for as long as possible so your opponent being able to stay locked is a big deal. Of course if you can hold them up for a further turn then great. The big issue is that it's not like you have a unit you can charge in to save the warriors if you need to.
Anyway, the other big change is Supporting Fire. This doesn't seem all that dramatic at first as it's only 6" and of course it's BS1. There's been much excitement about markerlights modifying this but I'll discuss that more when I talk about pathfinders. The key thing is that if you combine Supporting Fire with an Ethereal and/or Fireblade then it can start to get really painful. A unit of fire warriors being charged can potentially put out 48 shots meaning roughly 5 wounds on MEQ. Assuming a couple of kills that can often be enough to prevent a charge. Add in another couple of nearby units who are also affected by the Ethereal and there's the potential to kill a unit in the opposing players turn. Awesome.
Let's not get to carried away though. This assumes that your opponent is charging only a single unit surrounded by other units. In practise, they're likely to be making several charges so you'll need to consider where best to use your supporting fire. A good opponent will force you to decide the order of Overwatch by planning his charges.
Coming back to markerlights for a second. A full squad of pathfinders should be laying down 5 marker hits which means, for example, BS6 fire warriors with Ignores Cover. This isn't really anything new except that there doesn't seem to be an upper BS limit and even the best cover saves can be removed. This really needs to be factored in when discussing Fire Warrior effectiveness though. That 48 shot unit at BS 5 would deal out around 25 wounds to MEQ which is pretty much a dead unit of anything. Even without the Fireblade/Ethereal they're pretty lethal.
Given the amount of fire a single model can produce and their relatively poor durability I'd say a few units of 12 fire warriors is the order of the day. If you aren't fielding an Ethereal (more on them soon) then I'd suggest a Shas'ui for the Ld boost but it's debatable whether the markerlight upgrade is worth it if you have pathfinders. Bonding knives aren't worth it. Paying 12pts to save potentially 2-3 fire warriors is a waste in my opinion.
Finally, I wouldn't suggest EMP grenades or drones. The drones don't do anything a fire warrior doesn't and you're better using the points on another unit. The grenades are incredibly situational for 24pts per 12-man unit. They aren't bad for walker protection but if the walker has gotten that close unscathed and been allowed to charge then there's something wrong.
Devilfish
On the expensive side at 80pts and even more so with a disruption pod now costing 15pts. There's still a case for taking these for your fire warriors. The burst cannon now fires 4 shots and the drones get two each which is pretty impressive firepower for a transport. The drones still die with the transport but can be detached easily and won't give up an extra VP. There's the option to upgrade the drones to an SMS but 10pts is a lot to pay for BS3 and Ignores Cover in my opinion.
Bear in mind that the transport capacity is 12 so you'll have to lose a fire warrior to stick a Fireblade in there. Since his boost relies on the warriors not moving though I'd say he was better without a 'fish. Otherwise the old fish o' fury is alive and well even if it struggles for range thanks to the rules for disembarking from transports.The disruption pod is the only upgrade I'd go for. It gives a pretty much permanent 4+ cover save and the 12" range limit has been removed. The other upgrades start to make the 'fish too expensive or simply aren't much use.
I'm not sure there's much benefit in taking a Devilfish for all your fire warrior units. The costs can soon rack up and most of the time you want them shooting rather than hiding in a tin can. In these days of plasma spam AV12 with a 4++ save is pretty solid though.
Kroot
Kroot got hit hard by the new codex. Whilst they're a single point cheaper they lost an attack and are now S3 instead of S4. In the old book they were hardly combat monsters but now there's no debate about rapid firing or charging. They're still good for cheap objective grabbing and with careful objective placement they can be made pretty useful. They get a token 6+ save for which they needed a shaper and had to pay before.
The precision rounds are a bit of a strange one. Against most units the 4+ to wound is no better than the normal round. However, stick them in cover somewhere and target MCs and there might be a case for 1pt per model just for the opportunity. Realistically though you're not getting many hits with BS3 so even the minimal cost might be over doing it since you lose the half range bonus shot.
Interestingly it's worth noting that the Ethereal also effects Kroot rifles with his bonus shot "power" so bear that in mind when deploying.
Conclusion
With the reduced cost, free grenades and bonus from the Ethereal, Fire Warriors are likely to replace Kroot as the go-to troop choice. There's still a case for Kroot as "bubble wrap". The new codex certainly didn't make one far better than the other but I still feel Fire Warriors have the edge.
Right, next time I'll be talking about the Fire Warriors' cousins the Pathfinders. In the meantime I'd love to hear your thoughts.