Answer is NO. ASO in CSS is much better than AAO.There is no promotional avenues down the line.... from 4800 gazetted to beyond 5400 PB 3 till retirement. However every ASO reaches to Deputy Secretary..many reach Director and a very few to Joint Secretary level. AAO has frequent transfers while CSS is located only in Delhi which is very detrimental if you plan to prepare for IAS or otherwise too. Higher ranks of CSS are powerful and respected as they implement/monitor the policies of GoI in all over India. If transfer is not an issue Examiner, ITI, AEO are much better than AAO in the long run. I have talked with a few AAOs myself and found out this....you may cross verify rather than wasting ur career and repenting later....I know people who have reached only 5400 after 25 years of service.