If you compare between IAS and IFS then obviously IAS have more authority in the district and the public administration compared to IFS. Although for IFS, the country in which the officer is posted, becomes the diplomat who is responsible for the well being of the citizens of India living in that country and the officer becomes a authority and representative of Government of India in that country. So they have relative strengths of authorities.

Now CBI is an investigative agency mainly working on Corruption, Smuggling, Anti-terrorism etc. Now if a CBI officer is given the right by the Supreme Court of India for Investigation for a case related to a Public Administrator then yeah! then CBI will feel more authority to question any IAS and officials.

In general, the people think of authorities but when you become an officer, this things doesn't matter. If you are enthusiastic about the work then go for it and you will really like the job not for the authority but for the job.

To know more about UPSC visit the link below:

https://competition.careers360.com/exams/upsc-civil-services-exam

I hope this answer helps. All the very best for your future endeavors!