You'd have to know the opening in order to know the statistically best defense for it. So pick an opening move (e4, d4, etc...) and you can find your answer here:
http://www.chess.com/explorer/
http://www.chessgames.com/perl/explorer
Please note that you need to have some reasonable number of played games in order for statistics to "work". For example, based on chessgames.com opening explorer one might make a conclusion that 1... h5 is a best defence to e4 and d4.
which defence is the best statistically??