There are some people who says you should stay with R12 and some people go with r134. It is your choice.
I did convert to r134 no because of the price but the uncertain availability in the future. When you replace the evaporator the cost of the freon is not too bad and the system has to be open and evacuated so, why not do it?.
I live in Florida and the cooling with r134 is OK. The main thing is you have to have a properly "working" system.
You will hear different arguments but the final decision will be yours. Do some research and then go for it!