Dear Guruji and Jyotishas,
I tried to see how often does a graha get retrograde. I tried an everyday position for 60 years (21914 days) period. Here is a summary.
You can note that Venus is lowest, with only 7.3% times being retrograde and Saturn is retrograde most often times at 36.36% times.
The order is of how often a graha gets retrograde is not in any particular order in when seen as a whole. But, The outer planets are increasing order and inner are in decreasing order.
NOTE: If any one is interested to verify the data, It can be provided on reques or the method to generate it.
The following command was executed using the swiss ephemeris command line test program
swete32.exe -b1.1.2007 -n21914 -p2 -g, -fPYls >Mercury_Speeds.CSV
The above was redirected to a CSV file.
The -p2 was done for values from 2 to 6 i.e Merc to Saturn.