which is better ias or cbi and which is more powerful and prestigious

IAS is definitely more powerful, since they control whole nation in every ministry by becoming secretary. IAS also heads home ministry which controls CBI and other many departments.

OFFCOURSE CBI BECAUSE THEY HAVE THE POWER ON WHOLE INDIA AND IAS USE TO HANDLE ONLY HIS PLACE WHERE HE IS APOOINTED THERE IS NO WAY TO COMPARE THESE OFFICERS BUT ULTIMATLEY CBI IS INDIA BEST INTELLIGENCE ANGECY!