For 75 Points you get a squad that can rip up (almost) anything that can come in their way! Drawback:Weak Armour Warp beasts have no AP
A heavy-duty HQ choice.
Weakness:Ranged Combat
Some excellent Elites.
Weakness:armoured opponents
A  Super (Heavy) Support Choice.
Drawback:Slow!
A typical Troops Choice.
Useful for Cover Fire and Bullet Soaks. Weakness:Assault
A fearsome Fast Attack choice.
An anything but tranquil transport.
These units are all good in their own ways. If your opponent had a fearsome Chaos Sorcerer, a squad of Mandrakes would be good at stalking it. However, if they commanded perhaps a large number of Khorne Bezerkers, more Scourges giving support fire would be needed. I am using Chaos as an example of what would be good against various units because I play against Chaos armies frequently.