I've always had great luck with Knox gelatin as well as generic versions.
I've made my own hide glues as well using sinew scraps. I prefer the baking method since I don't have to watch the pot so close. Put your sinew scraps in an oven approved baking dish, cover with distilled water (not necessary, but why add minerals that might weaken the glue), put the cover on the dish, and put in the oven at the lowest temp it will operate at. 6 hours is good, 12 is better. Just check once in a while and add more distilled water as needed to keep the sinew covered. Strain thru cheesecloth or a fine wire mesh strainer into a shallow pan and let cool.
I usually freeze it then, but in the past I have cut it in very thin strips and put it in a cool place with a fan on it dry it out. If you choose to freeze it you don't have to putz with re-hydrating!