I use both....
Although they're both liquid scuff/sandpaper products, they're different enough where they actually compliment each other. Storm React Scuff, which is more of a gel, is the more abrasive of the two. It reminds me of NeoTac Liquid Sandpaper on steroids. I really have to be careful to not dull the ball up too much when using it.
Motiv Scuff is less aggressive (given the same pressure), but still effective. I find less is better with the liquid products. If I want more aggressive, I use Abralon on the spinner to get a more uniform result. Another nice feature of Motiv Scuff is that you can leave a thicker application on the ball for 30-60 minutes and get some oil extraction. The thick paste solution dries and sucks oil out in the process. Wiping off the resulting powder residue is a little messy, but it seems to work.
They're both good products that provide the same basic scuff feature. You can't go wrong with either. They're cheap enough to try both and make your own conclusions.