Which cam is best for Snorkeling in the Maldives?

This resort on the maldivian Island of Dheru is called "Jawakara" and was the best island we explored so far (actually it's two islands connected via a 600m long bridge). 

Best SETTINGS:
4k30 or 60fps  (30 for low light)
4:3 aspect - so you can re-frame if you didn't have your subject centered well
Rocksteady stabilization on, wide FOV
Option: underwarter color 

TRANSFER speeds:   
  Nano (128gb version):    ~500 mbytes/sec !!!
  Action5 (internal mem): ~300 mbytes/sec 
  from SD card:                    ~80  mbytes/sec

BATTERYLIFE: 
really good efficiency! Action5 runs very long, little Nano runs "long enough" and is re-charged quickly with it's screen module...
Never was an issue in our 2 weeks of snorkeling!