I think beef heart is the better one. Only thing is when you feed it too your fish(fahaka I assume) it makes an incredible mess outta your tank. Generally from what I have heard, beefheart is used to feed sick fish and or the big predators. Personally I wouldn't feed it to my puffer but that is just my opinion. Be patient dude your puffer will grow lol Just keep feeding him everyday and he will sprout up good. Get ahold of Mykiss if you haven't already, he sells ramshorns real cheap. Another thing you can try is stuffing frozen prawns with some kinda pellet like massivore which might help growth and soak the food in some vitamins. Also with beefheart you need to make sure all fat and sinew is taken out, bad for fish.
I've feed my arrow,dats and cichlids beef heart. It really makes a mess of the tank. It's only good for fish that have really big mouths that can eat in one gulp and won't spit it out or chew it, like many fish do. This is why I only feed beef heart to my electric eel. He can get it on one gulp and it doesn't make a mess. Maybe not the best choice for a puffer b/c don't they like to chew their food?
I second --the heck of a mess notion. I used to feed it to my large cichlids when I was a teenager. I had some success food processing it and feezing it in cubes with spinach and fish. Still messy though and, to me, it smelled bad (baring in mind that most fish food doesn't smell wonderful)