Full disclosure, I sell OSR2+s, so please take my perspective with a grain of salt.
I agree with @GarbageMan that the Tempest machines are my favorite. Not only because of their functionality, but also due to their customizability.
Their compatibility with MultiFunPlayer which allows for an incredible amount of customization and tuning from a software perspective. Setting generated multi-axis movement, length and speed limits, etc. allow you to have the toy’s performance match your exact preferences.
From the hardware perspective, they’re equally customizable. They’re compatible with a wide range of sleeves to match your exact needs or fulfill desires to experiment with different products on the market. And lastly, with the OSR2 and SR6, you can customize even further with servo selection. Servo attributes such as speed, torque, and noise are all on the table to customize to your preferences.
For me, additional axis movement is hyper important. Going back to single axis toys feels very “dead” and unrealistic. Even a small amount of generated motion on additional axis makes it feel so much more natural and realistic.
Lastly, between the OSR2 and SR6 - a hotly debated topic - I definitely lean towards the OSR2+. I’ve posted my thoughts before on this here - OSR2 or SR6? - #4 by g90ak