Over the years I've talked to AC pros like the vendors of AC service equipment at SEMA. They all consistently say to stay with R-12 as long as it is available. This above is primarily due to the loss of cooling capacity that is inherent when systems originally designed for R-12 are converted to R-134a.

Also, there are huge stockpiles of R-12, but fewer older cars that use it due to conversions and just lack of willingness on the part of owners to spend money on any AC service for older cars.

As a result, they predict that the price of R-12 will continue to decline.

Duke