Since I'm a cheapskate I've tried the cheap ones-blah-the Classic Equine have been hands down tough. OR I like the old fashioned nets but you have to know how to tie them up so a leg doesn't end up through it.
There were some made in pinedale wyoming for a while that were tough!! I thought they quit making them but maybe not. http://www.foldafeeder.com/Dealers.html
Classic equine has some that are the same style. I love how easy to fill they are!
I prefer the Classic Equines....my guys go through haybags like no other and the CEs have lasted the longest. I also like the slow feed nets....I just need to break down and buy the good ones that they won't chew through in a weekend.