MaxiFrig is a replacement refrigerant that is compatible with both r12 and r134 oils. It runs colder and operates at a lower pressure than the r134, so it is easier on the compresor.

I posted a comparison here Maxifrig vs R12 last year. There are some links to other BB's where the different types of refrigerants are discussed. From what I understand Maxifrig is a carbon(propane) based refrigerant, which has given some people misgivings about using it in their car. However the amount of propane used is small enough that there is little to no chance of a fire being caused from a leak in the system. Furthermore, since propane has an odorant added which is easily detected by the the human nose, any leak inside the cabin should be easily detected by the occupants unlike the r134 or r12, which have little to no odor at all.