thats a lot to answer in one post,
both are good at doing there intended job, if you turned up with just longnets and found a 4 holer, you'd be f*cked really, and the same goes with purse nets, turn up with 25, you'll need 35 or a long net,
so get both over time, by the sound of it, from what your asking, your a total newbie, nothing wrong in that, if you can find someone local to you, that can show you the ropes, get in there,
asking the above question, does that mean you already have ferrets??, cos if not, you'll just need a long net, and then look in the long netting section for