The Kelvin value is the colour temperature of the bulb and has nothing to do with the intensity
It all depends on your preference:
6500K Yellow, High PAR, More growth of corals
10000K Cool White, Medium PAR, Resonable growth of corals
12000K Cooler White, Lesser PAR, Lesser Growth
14000K Bluish White, Lesser PAR, Lesser Growth, Colours more vivid
20000K Blue, Very low PAR, Low growth, Colours more vivid