R134 is not as efficient as R12. It requires a larger condenser and evaporator to match the cooling power of R12.
Duracool is a propane based refrigerant that is more efficient than R12, and has been approved by most countries. The US hasn't approved it because of volatility concerns in motor vehicles (that pack around a tankful of highly volatile and explosive gasoline). David (Carolina_Mountain_Mustangs) has tried it and really likes it. Individuals can order it directly online. You can read more about it here:
https://www.duracool.com/