I work with a small non-profit - I need to calculate percentiles for a number of fee ranges, i.e. what is the median fee charged, 45th ptile, 55th ptile etc. in different regions of our state.

I've been looking at http://www.wessa.net/quart.wasp which calculates percentiles or quartiles by a number of different methods. I know there is not consensus on a "best" method, but is there a most common method or methods? Is there one that is particularly appropriate for small data sets? Is "Closest Observation" an acceptable method? Is Weighted Average at X(n+1)p preferred over Weighted Average at Xnp or are they equally okay?

Sorry for naive questions, thanks for any help!!!