While the Commander is no longer a must-take in the Tau army, I think it's still the single most flexible HQ choice by virtue of its many options. Between weapons, support systems, and signature systems, you can kit out a Commander to serve a variety of different roles. Here's three Commander builds I'm kicking around, all of which serve completely separate roles in the army.
The Hunter
Commander with Puretide Engram Neurochip, Early Warning Override, Velocity Tracker, Plasma Rifle, Fusion Blaster - 155 pts
The Hunter's job is to seek out foes and kill them with superior high-strength/low-AP firepower. He has the Puretide chip to let him switch between Tank Hunter and Monster Hunter, depending on what his opponent has brought to the field. The Early Warning Override allows him to react to new threats on the battlefield, and the Velocity Tracker allows him to take on those threats that come from above. Combine him with a bodyguard team to help keep fire off of him, probably with velocity trackers of their own.
For an alternate build, try swapping out plasma for missiles to have stronger long-range shots available, or the EWO for a Target Lock to allow the Hunter to go after his own targets while staying protected.
The Warrior
Commander with Iridium Battlesuit, Shield Generator, Onager Gauntlet, Vectored Retro-Thrusters, Fusion Blaster - 160 pts
The Warrior eschews the normal Tau strategy of "peace through superior firepower" and instead charges directly into the fray. His suit and shield generator make him far more resilient than most of his peers, the thrusters make him faster, and the Onager Gauntlet makes him able to take out a variety of threats in a single blow. A Fusion Blaster rounds out his kit, allowing him to be equally effective against vehicles at range. He's not equipped for handling hordes, but rather for making precision strikes against key targets. A bodyguard unit with VRTs is essential for keeping up with him and keeping stray fire off of him. This build is a bit of an oddball, but it could be very effective in the right situations.
The Guide
Commander with Command and Control Node, Multi-Spectrum Sensor Suite, Drone Controller, Shield Generator, Twin-Linked Flamer - 163 pts
The Guide does not deal with targets himself, but rather joins another unit and improves their shooting ability. His two signature systems ensure that any unit he joins will be rerolling hits and ignoring cover as long as he does not fire in the Shooting phase; with his twin flamers, his fire is limited to Overwatch purposes. A Shield Generator keeps him alive longer, as do the models in the unit he joins. The Guide is best used joining a unit of Marker Drones to give you BS5 markerlight shots, but joining a unit of Pathfinders or Fire Warriors is also a very valid option.
Consider adding on drones of his own, whether markerlight (to add 2 more shots to the party) or shield (to provide some buffers at the front of the group).
I'm looking forward to trying out these various builds and seeing what an army built around each one would look like!