Hi All 

I've seen some drones with an additional hd camera mounted in the top front.

Which is the best type with a square shape not to be too big like a standard GoPro?

You probably won't find anything as good as a GoPro for the best FPV footage, but there are other options if you are prepared to make some compromises. I suggest you take a look at Oscar's comprehensive guide at the link below. I think he pretty much covers every possible camera that is suitable for mounting on an FPV quad...

https://oscarliang.com/action-camera

Does the GoPro hero 5 session have image stabilisation?
Are any of the thumb sized cameras as good?

(30-Sep-2023, 11:23 AM)PJKMBAKER Wrote: Does the GoPro hero 5 session have image stabilisation?

Yes, the GoPro Hero 5 has built in stabilisation capabilties and it also logs gyro data so you can use unstabilised footage with software like Gyroflow, however it should be noted that the recorded gyro data is susceptible to vibrations from the motors so it can be difficult to get decent results when trying to post-stabilise the footage. The GoPro Hero 7 Black also has the same issue, but surprisingly the GoPro Hero 6 doesn't. The GoPro Hero 8-12 are also fine with no know post-stabilisation issues.