[SpartanTau]

DEVILFISH TROOP CARRIER
Good:
- one of the best armored transports in 40k
- a Tau tank (access to armoury, skimmer)
- able to upgrade to a Warfish (Smart Missile System, Targeting Array), making the Devilfish a respectable gunship
- "Fish of Furry" technique (allowable as skimmers do not block line of sight)
- brings two free Gun Drones
Bad:
- only can transport two different units (Fire Warriors and Pathfinders)
- can only fit twelve models (full sized Fire Warrior squads can't fit)
- is a Tau tank
- expensive for a transport (usually between 90 and 120 points)
- main Burst Cannon weapon not very effective

Recommendations:
Devilfish should be left at home unless you are mostly or fully mechanized or you have Pathfinders, as they are required to take one. By only having a small number of Devilfish, it will be easier for your opponent to stop your momentum quickly, making your soft Fire Warriors that much more vulnerable. By taking a lot of 'Fish, along with Hammerheads and Piranha, your opponent's heavy weapons will be over taxed, allowing your aquatic armoured detachment to swim freely.
Taking Warfish (Smart Missile System, Targeting Array - 120 pts.), while very expensive for smaller games, turns the Devilfish into a very powerful gunship that can completely protect itself and still attack. This option is especially good for the mandatory Pathfinder Devilfish, as it shouldn't be transporting the unit at all (in the best situations), and paying 80+ points for something that sits in a corner is not good.
If you have massed Firewarriors, the basic Devilfish is the way to go. It allows you to still retain the protective benefits of Tau vehicles and the destructive benefits of Pulse weaponry. By keeping the cost for each transport low, you can use those saved points for more Firewarriors or heavier weapons.