I installed two new compressors, and used R414 as an R12 replacement. Both compressors (in a row, on the same vehicle) failed within 24 hours of being installed. When The third compressor arrived, the only thing done differently was that the system was charged with R134A, and the compressor is still in service 4 years later.
I do prefer Duracool as an R12 replacement, and I have a significant amount of experience with it. I have used sveral other products, as well, but the Duracool seems to work the best. I prefer it to RedTek for the fact that is has an unpleasant odour, so if you have a leak, you won't confuse it for anything else. I runs lower head pressures than 134a, and needs less system charge (by weight) than both R12 & R134a. I have serviced hundreds of sytems, and have had none fail or operate poorly due to the refrigerant.
IMO, retrofitting to R134a will leave you dissapointed with your systems performance. After testing several retrofits, and brushing up on some pressure/temperature charts, I have drawn the conclusion that due to it's lower efficiency, R134a was not a good choice for installation in an R12 system. The condenser and evaporator do not have the physical size to cope with the higher pressures produced by R134a, and results are poor vent temperatures. Newer vehicles have engineered the A/C system components to compensate for this, and they work well.