I needed some new boots for firewood working and picked up these Herman Survivors. One idea you might consider is coating your boots with a good layer of epoxy resin like this. I do it before waterproofing the rest of it. It really helps to keep your boots leather from getting all scratched up in front.
I've used different brands over the years for this, usually just what's lying around. I don't think it matters much as long as its a water-resistant/waterproof type. I prefer a slower setting one too, not a "5 minute" one.
They do seem to stay quite flexible. I checked my trash can and what I used was some "Gorilla" brand stuff this time, although I usually use "Duro" brand. They will get scuffed up over time but the beauty is you can just sand them lightly and apply another coat!
