The Tau.. here's my Strategy
The Set-Up
Get your Earth caste builder to build a plasma generator
while it's building, queue up a stealth team, another builder, jetpacks and 2 more builders
once the builder is finished with the generator, make it build another one.
when the stealth team is ready, send it to capture SPs around your base and fill in with ppl
send a builder to build listening posts on every SP they capture(add fortifications if it is in a dangerous place, or easy for enemies to attack)
when the 2nd builder is ready, make it build a tau barracks, use another builder to build a path to enlightenment, then a kroot barracks.
The Defence
train your commander
build 1 or 2 XV88 broadside battle suites, and entrench them at the entrance to your base(normally around a SP because of the fortification i mentioned earlier)
build 1 kroot carnivore squad and leave them in the centre of your base.
The Strike Teams
Tau
build a Mont Ka command post and research teachings of Mont Ka
build a vehicle beacon
build 2 Hammerheads
ammas as many Skyray Missile gunships as possible
ammas as many Broadsides as possible
steamroll from one side of the map to the other

(not very elegant, but it works)
Kroot
Build a Kyoun command post, research teachings of kyoun
build a coalition Centre
train a Greater Knarloc
train 2 kroot carnivore squads
train 1 kroot hound squad
train 3 kroot shapers
attach 1 shaper to each of the carnivore and hound squads you just made
build as many krootoxs as you want (i've never needed more than 5)
use these and your commander to strike the enemy
EDIT: note with the "Stirke Team" section, it's an either or situation, either Tau OR kroot