If they are working properly they should all give very similar levels of stabilisation. The differentiators include:
Robustness of construction - gimbals don't do well after a hard "landing";
If they are running genuine controller boards, not knock-offs;
Weight (but see my first point);
Power efficiency;
Utility (can you repurpose it on another aircraft, for example?);
Price;
Support;
Availability of spares (see first point!);
Upgradeability (3rd axis?);
... and so on!
For what it's worth I'm very happy with my Rotorpixel, but there are people equally happy with their Dronexpert gimbal, their chinese all-plastic knock-off SimpleBGC board gimbal, and everything in between. It's all about what's best for you, really.