My Two Labs Have Hip Or Leg Displasia And/or Arthritis

My two labs have hip or leg displasia and/or arthritis and vet at first gave tramadol...but, made one of them very anxious, etc. So, now we are on Meloxicam 7.5 mg, but one-half only, once a day. Seems to work okay, but the one lab seems more sensitive to drugs than the other. I just finished a large bottle of MSM I got at health food store and not sure if it helped or not.
Question: I was told to get "cosequin" instead of MSM. What brand if any is better...and what should I look for in quality? Ie. the best processing method for the product, etc.