Since I haven't commented on the last 47 iterations of this thread, here's my 02.  

I converted to R134a in 1998 and have been very satisfied. 

I can't argue R12 vs R134 since my AC didn't work when I bought the van.  I converted simply as a matter of convenience.  I was replacing hoses, reciever/dryer, and expansion valve anyway.  The only added items were a few O-rings and the compressor oil.  

My AC works great and I've added less than two cans (I think about $5.99 each) in six years.  

Beats the heck out of skulking around trying to find bootleg R12 or paying current shop prices for the "real thing".

Tom Marsicano
88 Westy