In my opinion, if you are starting the preparation of IAS Exam and still confused about optional papers don't opt either Geography or Public Administration.
These papers are not high scoring papers in general; if you look at marks obtained by candidates in these two papers you won't find it worth the effort they put in while preparing.
The number of guys opting these two papers are highest, and because of this bar is getting higher every year.
For example, even after getting selected once for IRS with Public Administration, last year's topper Anudeep changed his optional paper in his attempt.
I am not saying you must not choose these papers. In fact, you must opt any of it in case you like a lot, or you have some academic background related to any of these.
But if you are equally bad in all the papers don't go for these two.
Find a better alternative.