Nowadays PCB manufacturers such as PCBgogo offers many option for PCB surface finish, called the plating process.
There are lots of different type of plating finish that can be selected depending on the application.
The most popular, HASL (for hot air solder leveling) is the cheapest option but lacks the precision required for fine pitch automated part placement since the leveling is not uniform
The second option, ENIG (Electro-nickel immersion gold) sometimes requires a little fee but the precision obtained using this process can be used for high density automated placement and relow soldering PCBs
If developing RF boards such as RF antennas or any PCB requiring constant dielectric property, the OSP (Organic solderability preservative) plating is the right choice because it won't affect the dielectric property of your PCB and will also protect the exposed copper from oxydation.
Hope this article was useful in determining the appropriate surface finish for your next PCB project!