Both the jobs are very good, now if somebody have a choice to opt following points should be considered b4 making a decision

1- Peace of mind.
I think that the anti narcotics force is a law enforcement agency and therefore the job is full of challenges and pressure from the high ups politicians and smugglers and so on where as the job of passport may be comparatively peaceful

2- Per motion
it is most important factor you must rule out the service structures of both the jobs as which job has rapid per motion .
3-Financial benefits
As AD passport there are chances of posting abroad and therefore it appears that the financial benefits may be more in the Passport department.
4-Easy Money Now it depends from person to person, in opinion the easy money is much more in narcotics as compare to Passport so should also be considered b4 making a decision.
5-Scholarships and chance of study
I think that there will more time for study available in Passport department as compare to narcotics department where you may always be posted at the small stations away from the main city which results into less opportunities to study further. I have heard that the FIA and passport people may get scholarships and leaves for further studies etc..... Check it out( I am not confirm)
6-Rum rations
I think that both AD narcotics and AD passport have the official vehicle petrol , telephone etc mark this difference as a factor in your decision making
7-Fmaily life:
Please check it out that the family life and the education of kids would be better in which department.

Rest you will have to go for which appeals to you. Best of luck where ever you go man........!!