Tek Turret/Heavy Turret [PC Small Tribes]

Best for base defense. 
Heavy turret is best if you haven't done the boss for the engram to use tek turret (needs electricity to work). They also deflect grenades, rockets and guided missiles, something the tek turret doesn't do.
 
Tek turret is the best turret but you can only use it if you have the engram (requires tek generator to work). They are also pretty good at dealing damage and filtering creatures you don't want to shoot.