Sorry I couldn't furnish you with reasons why I rate CSS better than PMS. The reasons for me are, first, promotion in CSS is twice as quick as PMS,second, CSS is national service whereas PMS, provincial. Besides, i've come to know by word of mouth that each and every group in CSS has some positives attached to it. Like DMG/PSP etc. might wield power, OMGians get promoted to Grade-18 within two years of their service. As is the case with postal. I heard someone say that postal group wallahs can give jobs/induct people upto grade-7 in their deptt.

To know more about PMS and CSS and to know which is better you might want to visit threads by the names 'css vs pms' and 'css or pms' on this forum.