That's what my guy said too. He'd go back to R-12 in a heartbeat. But from what I read the new R-1234yf is better than them all, uses less at slightly higher pressure, and is way down low on the greenhouse gas list. The limit is 200, R-134a is like 1200, and the R-1234yf is only 4. Mercedes was developing a CO2 system and it was great as far as a greenhouse gas, cost, and supply, but the operating pressures needed where extreme so they gave up. But the R-1234yf is going to need totally different recovery/recycling equipment as even the PAG oil will be different too. I even read that they may outlaw anyone from servicing the new systems or converting old systems unless they can prove they have the proper recovery equipment. They really don't want anyone venting the old gas to atmosphere, as DIYers tend to do.