I'd avoid plastic material because fish always rubs against it and it may get injuries. Cloth net is better because of this reason (I've seen some tench that have been in trap for ~1 week. I can't even imagine how could they look like after one week in plastic trap...). By the way, stiff plastic funnel is easy to get in and not hard to get out too, but loose funnel is easy to get in but hard to get out.
If your planning on leaving traps in for a week then by all means use cloth netting, my traps are never in longer than overnight and are simple to make, cheap and in my experience very effective in small ponds and streams.
