Listed below in no particular order is an overview of the various turrets you can use when you have the required funds to purchase them.
Minigun
This turret is a versatile weapon that can attack both ground and air units. Very useful in many missions.
Sub-Zero
This turret sprays cold ice, deal a small damage and reduce movement speed of the monsters with it's blast radius. Reduce 30% movement speed.
Disruptor Laser
This rapid-fire turret can target both ground and air units. It is also useful against fast monsters.
Rocket Launcher
A turret with high attack range and it can attack both ground and air units. Effective when against mass monster.
Electricshock
This turret can attack 3 monster at once. It is very useful when against mass ground monster.
Flamethrower
This turret can deal massive damage to ground units. However it is not very effective when against fast monster.
Sonic Blast
This turret has high attack and large blast radius. However, it needs more time to reload than others. Can attack both ground and air units.
Missile Launcher
A powerful turret that shoots 3 non-guided missiles. It is slow to reload but have large blast radius.
Disintegrator Ray
An upgraded laser turret. It can deal massive damage to both ground and air units.
Toxic Dispenser
This versatile turret can deal massive damage and slow many monsters at once. Reduce movement speed.
Omega Cannon
Very powerful turret that shoot guided missiles. It also has very high attack range. It's only weakness is high reload time.
Paralyzer
This turret can unleash energy waves that will paralyze monsters around it and slow them down. However it cannot inflicts any damage to them. Reduce movement speed.
Enhancer
A turret that can link itself with 1/1/2/2/3 nearby turrets and increase damage of them by 10/20/30/40/50%.
Ballista
A turret that only attacks air units and can slow them down in a short duration. Reduce 30% movement speed.