I think this is a good question that goes beyond a one word answer. There are lots of joint supplements on the market, and most of them are not "cheap". However, there is conversation that needs to be had beyond the supplement itself.
I believe that the first thing before any selection of joint supplement is made is the issue of buying a sound steer to begin with. A joint supplement will not make a crippled steer sound. It may "keep him together", but it won't make him sound. A joint supplement WILL however keep a sound steer sound through the process of stress caused by travel, wash racks, being tied in a cooler for 4 months, up and down, standing in a blocking chute for hours and hours at a time, etc..
The second thing that is important is exercise. Even a sound steer that is getting a joint supplement must have some type of an exercise run or pen big enough that he can actually get up a head of steam and get stretched out. He can't do that in a box stall. I believe that is really important. It is very tempting to keep them in a confined area because it is so much easier to get them soft and fat. But it is really hard to keep them free in their movement when that is done.
Next is ration. A really hot ration can cause the appearance of soundness issues. Lots of tightness in tendons, causing "popping" and things like that. The exercise helps that, and cooling their ration will often times eliminate it. In my mind, I don't classify this as a soundness issue even though a judge may not like it. That might not make sense to you, and I will agree with you if you don't like that comment. That is just my opinion.
Now to the supplement. I am personally a fan of Natural Stride. It is easy to get. Most all show supply outlets carry it. You can use it on all livestock. It smells great, so getting a steer to eat it is easy. I talked to everyone that we have bought steers from, and some of these sellers have had major success. Every one of them said to use Natural Stride, and no other. So my advice is based upon the opinion of the people that have won Denver, NAILE, KC, AK-SAR-BEN, Fort Worth, and on and on and on.
But again...It is not cheap!