which one for filming the action of catching BIG bass ?

If you're gonna wait until the fish is on to get the video, a phone may be best (if the phone has image stabilization). If you want to be recording when you set the hook, use a gopro.

There are many pros and cons for both. The mounting system is why Gopro is famous.

If you get a GoPro, you can count on the battery dying right before you set the hook....

Now you know all the big fish in Athens died. but seriously, I manage a cell phone store and I struggle to get the GoPro on the mobile app to do what I want. I have reverted back to my cell phone.

GoPro mounted somewhere in the boat. Just purchase extra batteries when you get the GoPro. There are many different mounts. I clip mine on to the steering wheel and film my fishing that way. Takes excellent video.

Plenty of other cameras that do the same for less. I have a Go pro, thinking of getting another non Go pro for less. But a Go pro style of Camera is what you want. The video editing is the big piece.

I'd go with Go Pro and get a 12v battery adapter and plug into 12V receptacle on boat.

Go-Pro. If it goes in the water it still works.