i do both atm, it depends on personal choice, if he prefers one then stick with that. but if its not that simple then he should consider how much effort he is going to put in. its very easy to get 80s/90s in SS with little effort and the paper has no essay style questions so is a good choice for those who are happy to cruise. i'm not sure how well it scales but it doesn't scale as well as geo. If he is happy to learn his stuff and commit to geography he can get better called marks with only a bit more effort, but essay writing is required....
So in summary,
SS= No essays, short answers only--more simple/less work..lower scaling
GEO= 3 20 mark essays + short answers--more advanced/more work.. higher scaling