In an Urban environment, post SHTF, the biggest threat there is the other survivors.
There are only 4 options.
1. Hide from them.
2. Join with them. (find the strongest, most providing group you can)
3. Fight them. (usually won't end well, and risky)
4. Run. Go somewhere THEY are not.
For my money, I'd go with option 4. Even if you hide, eventually you will open yourself to more and more risk as resources dwindle. Even if you join or fight, there will always be others that will fight as well.
As for WHERE to go....go rural. Nicer, more community minded people...who will welcome your labor in exchange for resources.