See both the posts are good and the pay scale typically the same. Now in Railways, the recruitment process is a bit longer and the notification of vacancies are irregular. Where as for the FSSAI every year the notification comes out. Also the promotions are faster in FSSAI compared to that of the Assistant Section Officer in Railways. Now the facilities are better in the ASO like it has free train allowance, education of child allowance which are not in FSSAI. So both the post good with there own demerits and merits. Now you have to choose on the basis of your interest.

Have a great day!