In 6e, the Tau Codex is rocking.
But it suffers from Older Codex-itis at high point levels.
Though by high point I mean over 1500 but below true 2000.
I've posted my list building else prior, so here's what I'm using for allies:
Codex Shopped Vanilla Marines, Blood Angels, Eldar, Dark Angels and finally came to Space Wolves.
Why Space Wolves?
Aside from being 1 point cheaper than their brethern they have great heavy support.
Madness you may cry from behind your keyboard, Tau have amazing Heavy Support!
Kind of. Hammerheads are now good with a 2+ save but with the wane of mech on the table everyone wants to burst their melta all over my armor 13.
Broadsides are still amazing, 10/1 will never be bad. In 5e I packed everyone I owned into a list.
But after they Demech your opponent or blast the Land Raider or Monolith back to the Craftworld, they're really expensive snipers with 1 shot each. The Hammerhead's pie plate is better but not twinlinked.
I've scaled down from 3 squads of 2 because there is just less armor to nuke.
What Tau are lacking in a point efficent manner is MeQ killing power.
Plasma-Flamer or Plasma Missile suits are great, but for the plasma to be effective you need to be up closer than you want.
64 Points per 2 shots of Plasma for a Crisis Suit @ 12 inches away.
That's expensive. Which is Why Space Wolves!
Cause they can take Plasma Cannons in a Dev Squad.
Also a Librarian with Jaws of the World Wolf and Living Lightning.
So instead of taking an ally that can give me assault protection, I'm taking an ally for more shooting.
Hail Beserker Space Viking Werewolves!