Hello Sir, I work as an auditor in CAG Audit. .Should I give IAAS as first preference in UPSC given the less hectic and apolitical nature of the job?

I would not recommend it.

There is no doubt that IA&AS is an excellent service. I have dealt with this aspect in another answer. However, your first option should be based on your aptitude and your aim.

I had given IAS as my first option, and would still give it as my first option if I were to fill my DAF now. This is because I started writing the exam with IAS in my mind. The executive power that you get in IAS is still something that other services can’t match.

To make it short, your first preference, should be based on your aptitude and your long term career goals. If IAAS is the job that you like, then you should go for it. I can’t comment on it because I don’t know you personally. But from a general perspective, IAS is still the best first option.