This is just a quick mechanical overview of the mechs, if you are lookign for lore-filled in-depth descriptions, you can find those in-game.
Junk MechThe Junk Mech is an underpowered meatshield, not a fun thing to pilot.
Standard MechA weak yet cheap mech, and relatively a vast improvement over the Junk Mech; in large groups, they can overwhelm small ships, though it is recommended to use them as support for tougher mechs.
Missile MechSlow and poorly protected, the Missile Mech carries two huge payloads capable of disabling the shields of even the largest of ships.
Mediant MechA standard mech with toughened armour, two small missiles and improved machinegun.
Triton DefenderAncient mech from before the collapse, can be picked off with long-range weapons and AA guns, but will tear apart anything in its range.
Steel ClampHigh armour tank designed to harass enemies.
Nimble MechLight transformation of a mech, perfect for bothering large targets.
Twin MechWields twin railguns, which are rather underpowered, but makes up for it with survivability.
Star DrifterGigant mech with very high armour and a fair arsenal, great in combat when not constantly retreating.