There are three things to consider when choosing a cast net and all three will effect how well it traps bait.
1. Depth of water, deeper the water the larger the net will need to be.
2. Weights, a good cast net will be real heavy to sink quickly.
3. Mesh size, if the mesh is too small the net will not exhaust, the weights will sink and the mesh will not allow the water to exhaust thru the openings and there fore mushroom.
I carry 3 on my boat, all are 10' with the largest amount of weight per foot possible, they are made by a company called Guideschoice.
Disclaimer.....this info is for the baitfish here in the northeast, down south the bait may stay on the surface and not beat feat to the bottom to swim out of the net.
Hope this helps.