And which is the safest?
I would say Libertycity from GTA 3 is the most dangerous and deserves its title ,,the worst place in america'' more than anything else.
There are aggressive gangs spread all over the city and nobody can drive and the police will more likely run you over instead of actually helping. When i had to live there i would lock myself up in a apartment and never leave it again.
Las Venturas in SanAndreas seems to be the safest city. There are no gangs and apart from CJ nothing bad can happen to you. But there are still lots of bad drivers who might run you over or kill you during a car accident, especially the police when they chase someone. So you should avoid the roads as much as possible...