Hi, I think you can search the forums for views on both the brokers .... my personal opinion is choose a firm which is more transparent in all its charges .... so don't hestitate in asking your broker for all the charges they will be levying and all the hidden charges like annual maintenance fee and my personal advice would be get it all in writing ...
Coming to your second question you can open as many demat accounts you want as all of them would require you to furnish your PAN card so basically even if you open 10 accounts they would all be linked to the same PAN number ... but my personal advice would be to keep just one active trading account and shift to another broker if you're not satisfied ...
Hope that helps