Technically, Butane has a boiling point of O degrees Celcius, so if it's below freezing outside, then your Butane bottle may struggle a bit to vaporise sufficient gas. If you are out and about on days like this - Propane is the only choice.
Propane has a boiling point of minus 40 degress, so even on the coldest day gas will still flow. But the downside of propane - and why you can't buy it in Southern Europe - is that Propane gas bottles can over pressurize on hot days (40 deg C).
So if you are out with the van when the temperature is above 5 deg C, Butane is the best choice.
Camping Gaz is butane, the only difference is that you can buy Camping Gaz bottles everywhere in Europe. Physically Calor gas bottles are different to Shell gas bottles, Elfgaz bottles are different again, etc., etc. So the supplier / refiller will only swap a bottle for one of the same make.
Suggestion:
1. Main bottle - Calor Gas Butane or whatever make you can easily get locally - and the best price too. Always use this bottle in preference.
2. Spare bottle (for Europe) of Camping Gaz size 907 (the biggest but still under 3kg of gas) - note that gram per gram this gas is roughly twice or three times the price of Calor Gas - then if your main Calor gas runs out in France - you can switch to this bottle and get a refill anywhere.
You can buy a Camping Gaz bottle adapter that accepts the Calor Gas thread - so you don't need a separate regulator - price around