HFC134a systems are a much bigger pain than CFC12, in any area that you care to name.

The molecule is much smaller, so it leaks much easier. Any moisture causes acid to form within the system, leading to much worse evaporator problems than you would otherwise have. The pressure readings are somewhat inadequate for judging the system refridgerant level - it's best to charge by weight. The oil used is hard to even call oil, and it certainly does not lubricate the compressor nearly as well as the mineral oil used with CFC12.

The only advantage that HFC134a has over CFC12 is that you can go buy it at your local discount parts house without a licence.