It's been a few years since I worked on A/C, however in Aussie R12 was banned and R134 was the replacement gas. It is not as good as R12, when I did a replacement I changed the compressor to a more efficent one and fitted a larger condensor ( the A/C rad. in front ) so that it would work close to the R12 systems.
At the same time a gas that has been around many years, ER12 was used much to Duponts discussed ( they had no patent on it ) and went straight into the old system and worked great. When any system has been opened or been used for more than a couple of years it is best to replace the dryer and "o" rings, cheap insurance, I did it automatically then.
Back to the ER12, the company manufacturing R134 did everything to discredit ER12 including making a film that showed a car being blown apart, of course when this was exposed as a fraud nobody could find the maker of this film. I'm not sure if it is still in use as I no longer work full time in the automotive trade.
I have seen Liquid Petroleum Gas used but that could be dangerous and when I came across it I had to do a complete flush and oil & dryer change before regassing.
R12 if used in a modern system would cool exceptionally well because of the different pump and larger condensor used, but alas it is banned.
More could be said but I'm not stupid and cannot put it in writing, just see how many times in the coming years these gasses are changed and who benfits from that change!!