Which brand of shark chondroitin is better for parents to eat, ask for recommendations

A **** to buy three kinds of parents, the following is the parents ate experience, does not involve advertising, according to the time to eat in order: the first is the aminosaccharine chondroitin (Japan), ate more than half a year, the elderly said that there is no effect, my father said that after eating the stomach acid and flatulence; the second is the shark chondroitin (Denmark's silver bottle), which has no merit; the third is also the shark chondroitin (Norwegian blue bottle), which has eaten the longest time, and the third is also the shark chondroitin (Norway blue bottle). Eat almost 3 bottles of the elderly said leg pain much better, can walk more, and now also go to the square dance than the scratch.