There's been some discussion of this over on the Hangar.
The Soldier: This is the design with the most basic loadout. One Direct Fire attachment, one Defensive attachment, one Spotting attachment, and one Movement attachment (2Rd/1B/1Y/1G/2W). It does everything, but nothing well. It was either created by Ced23Ric or Mechatonic. These should be filler units in your army.
Armored Spotter: One Defensive Attachment, two Spotting attachments, one free Movement attachment (1B/2Y/1Gd8/2W) This guy has one role; putting those big juicy yellows on the most opportune targets the opponent has.
The Blue die enhances survivability. Even still, keep this guy in cover, he has no weapons. This is the base version of the "Missile Monkey" described back in MD & TD 1.
Hammer: One Direct Fire attachment, two Defensive attachments, and one Spotting attachment (2Rd/2B/1Y/2W). This design and the next one are both created by Joshua A.C. Newman. They work together as a team.
Anvil: Two Direct Fire attachments, one Defensive attachment, and one Spotting attachment (2Rd+d8/1B/1Y/2W). The Hammer and Anvil work as a team. The Hammer drives the opponent before it placing spots for the more heavily armed Anvil.
Mecha Design & Tactical Doctrine 1
Mecha Design & Tactical Doctrine 2