Minnow seines should be no longer than allowed by law for bait-collecting without a collector's permit. I prefer nylon, which costs more but lasts forever. If you're stingy, get a cotton one. It won't last very long if you don't dry it after each day's use and hang it up where it cannot rot. The minnow seine should be tied to a pair of poles, one at each end.
Poles make a seine an easy piece of equipment to operate.
Without poles, you'll wear out your back from stooping. Poles are also the only way to handle a strong current, as in mid-river. Dip-nets should have a very long pole made of wood, not aluminum. They break almost as soon as you get them full of weeds. Search around for a good net that has no aluminum pole or collar.