What to use depends on your location.  What to avoid is called CL.

Makes NO difference really, other that avoid CL as keystone has indicated - main point to remember is that they should already be reviewed on TER!

I think it does differ from area to area which malls are more popular and have legitimate ads. Many of the small malls where the girls advertize for free you will find alot of bogus ads or out of date ads, hell I have seen some that had ads still up on girls that have been retired for a couple of years.  Most places Eros and Cityvibe are up to date as the ladies pay by the month, but you surely need to check the reviews on any lady there also.

They have about a dozen Ladies listed in their all escorts section who have either retired or done worse still on the PHX site.  Luck 4 us we have a trusted, and tried site in Phoenix411 here.