I'm doing Law, Economics and Gov+Pol at the moment for AS Level - Economics and Politics are seeming to work really well together, especially macroeconomics, so politics may be helpful with a bit of background to economics. Geography is also good, so maybe joint first with politics. And finally physics.
I'd do:
1) Politics (good spread and balance of subjects)
2) Geography (a lot of heavy humanities and heavy sciences (politics being a light humanity))
3) Physics (a huge amount of heavy sciences).
Either would probably be absolutely fine, but politics is good as it complements a lot of things and is just really good for general life.