Kraken Unleashed.
With units like the Argo Submersible Carrier they wold pose a really unique challenge to an invading unit that most probably wouldn't be ready for...particularly if Intel doesn't have them on planet. I mean, I wouldn't be surprised if it often happens that an invading force just does not include, or brings way to few torpedoes/similar naval weapons, as part of their inventory in their tightly packed Dropships.
..and Camacho's Caballeros/17th Recon Regiment...because everything about them reeks of awesome, and I feel Victor Milán really brought some flavor to the unit and the Trinity Worlds. You also have killer characters like Cassie Abtakha Suthorn, Marisol La Dama de la Muerte Cabrera, Rabbi Bar-Kochba, Colonel Carlos Tiburon Camacho, and Kali Dark Lady MacDougall. A unit with mech drivers so intuitive, they practice by playing football with their mechs, and can probably pull round house kicks on your cockpit in melee with ease.