Two source diode protection
Your first 2 options won't work.
Both of them will allow your regulator to be 'back-fed', which is usually not a good thing.
The other 2 will prevent the regulator from being back-fed.
If your load doesn't mind the higher voltage then the extra 3 diodes in option #4 are not all necessary, but you'll probably want to keep one of them unless you intend for your regulator to charge the battery too.