If you can afford R12 stick with it. I would have the front seal in the compressor replaced and all the o-rings and hoses.. fill it up with R12 and be done with it.

134a will work but it is not as efficient as R12 and the end result is higher vent temps. Some people are happy with it but I never have been. There are also some refrigerants available that are more efficient than R12 but they are propane based which could be hazardous to your health in an accident. Freeze12 is also an option for you http://www.freeze12.com/ Talk to the folks at www.aircondition.com before you make any decisions on how to proceed with the a/c work.... They have some incredibly smart people on the forum.

Good luck with your new ride!

Steve B.