There is no honest single “best build” before the full release. The strongest demo approach is to pick one damage identity, support it with grid-efficient modifiers, then add enough movement and crowd control to keep collecting XP.
Ranged control
Use a Laser, Long Cannon or Missile Launcher as the damage core, then add ranged amplification and fire-rate support. Keep coverage on more than one side.
Melee pressure
Orbiters and close-range effects reward staying near enemies. Pair them with movement speed and Repulsor-style safety so you can collect XP without getting boxed in.
Balanced survival
A mixed setup with one reliable ranged weapon, one close-range answer, movement speed and Overcharge support is less explosive but easier to pilot.
Why mixing matters
One demo player explicitly concludes that mixing different weapons is important because a high-damage beam can still fail if it only hits one direction.
Blueprint rule
Core damage first, then coverage, then movement/sustain. Do not fill the grid with three support parts before you have enough weapons to clear space.