Eleanor,
The one im using at the moment is a top and bottom pocket type and whether its prawns or bait fish it works a treat.
Ive never thrown a draw string type so dont know how they go but most nets are flat and if you are throwing it properly you should be able to get it to hit the water wide open and flat.
Have a look in the serch for cast nets and you'll find a heap of stories and also the guy on here that makes them...
cheers