Good thing about Nifty is that all options are very liquid.
Good thing about Banknifty is that because of the higher volatility, premiums are higher, so better risk to reward at times.
So you have to see the tradeoffs and chose what is that suits u.
You shall consider choosing Nifty or Bank Nifty depending upon which Indices you follow. Since both of them are very liquid, they are suited for options writing.
But the precaution you have to take care in writing options is the unlimited risk you are bearing with every position you take. So, be very precise about levels while shorting options. Though option shorting has a higher probability of success, don't take it as the holy grail. One wrong trade and it can sweep away, premiums of 10 trades!
So, start with writing very far OTM options.
Good Luck, http://www.traderschowk.com
my vote for nifty but far otm every month serise start after 1,2 days