In the same way that there are different grades of bolts, there are different strengths in pole. To maximize the strength of the pole, you want to look for the largest diameter pole with the smallest gauge.
While most people understand that a wider diameter will make the pole stronger, it can be counter intuitive to look for a low gauge number. Gauge is the thickness of the wall of a pipe or support pole, and the whole system is counter intuitive. A gauge 14 tube can have between 60% and 100% wider wall compared with a gauge 19 tube.
The exact thickness and support will vary on the other dimensions of the pole, but as a general rule of thumb for the average DIYer, when it comes to steel tube or pipes, higher diameter and lower gauge lead to better strength.