Go for the one with the longest warranty and if there is an extended warranty ,I would recommend you buy it.. Be sure you wire directly to the battery (with a CB or fuse of course). I read most 12 volt fridges are auto defrost, not frost free.
This cryogenic freezer from IVYX Scientific can precisely hold temperatures between +25.0°C to -86.0°C, in increments of 0.1°C. It uses a Stirling Engine for cooling instead of a traditional compressor, giving it higher efficiency, lower power consumption, lower weight and a smaller size...
ivyxscientific.com
Did you mean best or did you mean reasonable and usable?
Each of these were the "best" for the people that bought them - on the day they bought them.
You gotta define what makes your desired fridge the best.
Best fit to your space?
Best efficiency?
Best temperature control?
Best reliability?
Best availability?
Easiest installation?
Easiest to operate?
Best shelving options/flexibility?
Best door locking?