You may refer to the following article

http://scitation.aip.org/content/aip/journal/apl/75/22/10.1063/1.125377

Hello Arun! First these two settings of an AFM work quite differenty. K-AFM is a non-contact mode AFM designed to measure surface potential, while conductive tip AFM is operating in contact mode and is designed to measure the samples's conductivity.

Look-up the following links:

http://en.wikipedia.org/wiki/Kelvin_probe_force_microscope

http://ac.els-cdn.com/S0266353813004168/1-s2.0-S0266353813004168-main.pdf?_tid=46984028-39d0-11e4-af5c-00000aacb35d&acdnat=1410452923_aa0daad2aabab65fb9a2c9a1ad24d041

The KPFM is definitely the right method to measure surface potentials at the local scale. c-AFM gives access to local resitivity.