The public CQ WW CW logs allow us easily to tabulate the stations that appear in the largest number of entrants' logs. For 2016, the ten stations with the largest number of appearances were:
The first column in the table is the callsign. The second column is the total number of times that the call appears in other stations' logs. That is, if a station worked HK1NA on six bands, that will increment the value in the second column of the HK1NA row by six. The third column is the percentage of logs that contain the callsign at least once.
Tables for prior years are available here.
We can also list the cumulative data for the ten-year span from 2007 to 2016: