Denier is one of many ways to measure material strength, but should NOT be the only thing you consider. One brands slightly higher denier may actually be weaker than another brands lower denier. This is because the major brands use nylon or polyester as their base fabrics. A lot of brands only tell what their denier is and not if it is polyester or nylon. The type of material is as important as the denier, so you can compare apples to apples.
Polyester threads are less stretchy, but are weaker than nylon threads. Nylon is stronger, but more stretchy. Polyester cloth requires a higher-denier thread count than nylon to achieve the same strength.
This does not necessarily mean that one is better than the other. Half of the major brands use polyester and the other half nylon. The polyester boats are stiffer and more responsive. The nylon boats are more stretchy and bouncy making them less responsive in theory. Some people believe that the nylon is less likely to be damaged because of the more stretch upon impact and the polyester will have limited stretch before it tears. Personally, I believe majority of the boaters could only tell a slim difference in performance!
The amount of coating is important. You could have three different cloths with the same denier, but the overall weight be completely different. This is because one brand may have 80%, the other 50%, and the other 25% of their coating be the overall weight of the cloth. Again, another reason not to just look at denier alone.