I had / have a gas 3way, a Waeco and just got an evacool in our new CT.
Evacool the best one I've had to date for efficiency and insulation, but they're large and would need two people to carry if full of food. As stated, best for these to be fixed into car or CT and you won't regret having bought one.
Waeco in my car is ok for drinks and day trips/4wding at best. I find my 50l very much affected by the external ambient temperature whch in the car can fluctuate a lot. I find the food is either frozen as we travel with the aircon on, or defrosts/goes off as the fridge has to work so hard in the heat when no aircon and it flattens the second battery.
The new Dometic Gas fridges are very good on gas but best suited for a long stay situation in one spot, as said, not great when plugged into 12v.
I'm sure other's will have differing experiences, but that's mine to date.