I think you got three good answers from active commissioners which brings to mind something probably assumed in the replies but unstated: if you are looking for a good world to join, you need to look for a good commissioner.
Also, this is usually the byproduct of a healthy world and therefore useful when window shopping for a team...no dynasty teams that win 100+ games every season, and no bottom dwellers that lose 90 or 100+ games every year. That sort of competitive imbalance is almost always unhealthy. Frankly, the more teams that are actively attempting to win as many games as possible (and I am not talking just about tanking, but also coasting, or maintaining or "waiting for the prospects to develop" or whatever else you might want to call it), the healthier a world will be, from the free agent market to the IFA market to the waiver wire and the Rule 5 draft, everything. If you find a world where most division winners are coming in around 88-95 wins, and many of the others are bunched around a 375-480 win percentage, then the world is likely filled with committed owners who will help maintain the world's long-term health. This is not a universal, but I think it is a handy shorthand if you are looking in on worlds you might want to join.