While at the end of the day it does not matter what ball, you use as long as it is “round” as someone told me, there are differences in balls. Without getting too nuanced the Onix pure 2 was recently “banned” from tournament play. Why? It is very soft, the holes are bigger and it is considered too “slow” and too “forgiving” for tournament play. Most professional players have indeed complained and referred to these as “beginner” balls.
Just like the name implies the Dura Fast 40 is faster and livelier. If you are a hard-core tournament player, you are going to want to play with the Dura Fast or the Franklin ball as these are what are used mostly in tournaments. In addition, these are livelier, bounce a bit more and are indeed “faster”. These are also harder to control and thus offer more on the skill-based side of the game. (As opposed to more casual/recreational play.) The down side? The Dura Fast and the Franklin break sooner and in fact much sooner if it happens to be cold. On the rare nights when it is around then 40-degree mark these did break faster and in fact much faster than their counterpart Onix balls. These also break much sooner in terms of players whom are “bangers” so to speak.
The Onix balls are “safer” (softer) and last much longer and are thus more suited for longer rallies and are great for those interested in social or recreational play with little to no interest in tournament play.
Additionally, there are Jugs and Monarch balls. However, these are considered “cheap” and are not used very often.
Whichever ball you choose we are sure you will continue to experience the joy of Pickleball.