First of all, let me tell you one thing that you must have read or, at least, heard about both of those subjects through out your life, but in general way.

Now as far as the conundrum regarding the choice and the preference is concerned, I am more inclined towards International relations, for I actually like to have knowledge regarding what's going on in an international world. Who's is playing whom like a guitar, and who is being played by whom for what. Political science on the other hand deals "primarily" with the domestic politics, and I am kind of allergic of having something baseless in my mind.

The gist is that choose what you like; what fascinates you more. Scoring trend of 2014, on the other hand, dictates that International relations is more scoring than Political Science.

Regards.