1-wire really means the regulator is inside the alternator. Pros are simple wiring, Cons are the internal regulator is sensing the output voltage at the alternator terminal, not the battery. With a one wire you just want a good low resistance connection to the battery.
3-wire (external regulator) as installed on our old muscle cars really is not any better. The external regulator senses the voltage of the engine compartment wiring harness which can have a good amount of resistance to the battery. Most of the newer cars and trucks use the 3-wire setup because the computer can directly monitor battery voltage and both air temperature and battery temperature and set the best alternator output voltage to maximize battery life.