T'au need quite a bit of synergy in order to preform well, which I'm sure we'll all agree on. But how that's achieved is what's of discussion these days. There are several units that can help, several units that can do well on their own, and it's finding which ideas work best for you.
Here's a fun, and potentially deadly, idea of mine that I think you might enjoy (Or have already used in your own games).
Strike Team/Breacher Team (10 models max)
Pathfinders with specialized Drone
-The HQ choice is what ever you decide to make of it. But if you take the Cadre Fireblade, don't take any drones with it. I prefer Darkstrider, followed by the Cadre Fireblade.
-Depending on what your flavor of Fire Warriors you prefer will determine which you decide to take. I personally enjoy the Pulse Carbine wielding Strike Team for this set up with Darkstrider, though he works well with Breacher Teams also. The Cadre Fireblade can work better with Pulse Rifle Strike teams.
-The Pathfinders can contain as many models as you like, probably with Markerlights, but the idea is to take one of the support drones only they have access to. The Pulse Accelerator Drone is my personal favorite for this set up (24" Pulse Carbine/36" Pulse Rifle), but if you prefer the Breacher Team over the Strike Team, the Grav-Inhibitor Drone may be a better option to help stay out of combat.
-The Devilfish is rather obvious. Load up your HQ and your Strike/Breacher Team with the Drone you pull from the Pathfinders.
-Minimal build makes the unit cost barely more than 290 points.
This setup can be taken as part of a larger force to fill in a Battalion or Brigade Detachment, but it may be beneficial to take them as a Patrol Detachment depending on what your build is or what the T'au Sept (For Darkstrider specifically) special rules will be with the Codex release (When ever that may be).
The main goal of these units are to take out pockets of infantry that are holding an objective while being highly mobile and putting out quite a lot of accurate and better wounding shots. They can also be used for quick objective grabbing and a general nuisance. If you take Darkstrider, it can put him in a good position for spotting targets for your Fire Warriors, Pathfinders with heavier weapons, and Stealth teams while the Fire Warriors and Devilfish provide a screen for him.
The Devilfish should deploy with your HQ choice and your Fire Warrior preference embarked, and the Pathfinder Squad close enough for the Drone to move to it. The Pathfinders are there to provide Markerlight support for them later on, so try to keep them safe but in a spot they can see your target; they can move after deployment to aid in their safekeeping and leave the Drone behind.
The first turn should be the Drone from your Pathfinder unit moving to embark into the Devilfish, and then advancing as far as you can have the transport go. If you have a Commander of the same Sept starting next to it, using the Mont'ka ability to give it the extra benefit for advancing is quite nice. Until it gets to your movement phase when you want to disembark the units, just keep advancing the Devilfish to advantageous positions.
Once in position to disembark, have everything come out. Your HQ, your Fire Warriors, your Pathfinder Drone, and even the Devilfish's drones as well if you took them. Move into a more precise location, while keeping the HQ and Drone close to the Fire Warriors for proper support, and then open fire once it's your shooting phase. It should be devastating to most infantry units (May the dice be in your favor!).
-Darkstrider with Strike Team and Pulse Accelerator Drone: Lots of shots, regardless of Carbine or Rifle, with enough range to deploy earlier than later. Wounding T3 models on 2+ with Structure Analyser. Maybe use his Markerlight to aid for guided shots, especially if advancing with Carbines.
-Cadre Fireblade with Strike Team and Pulse Accelerator Drone: Good amount of shots at farther range with Rifles, but at least 30 (Not counting his own) when at 18" away from enemy. He can support with Markerlight or add his own shots into it.
-Darkstrider with Breacher Team and Grav-Inhibitor Drone: Better for later game deployment or hitting faster units hard. The closer the better to get use out of the Pulse Blasters; T4 models are being wounded on 2+, T6 on 3+ and T7 on 4+ at Close Range with Structure Analyser support. Darkstrider can use his Markerlight to better ensure hits, or to throw a grenade if close enough to lower effectiveness of counter attacks. Drone is completely optional with this build given how close you may end up disembarking may make it ineffective (Shield/Marker Drone replacement?).
I do hope that this has given you a fun and interesting idea for your games. If you're already running this build, I'd love for you to share your experiences with it. QCC welcome.