Unless you want to stay in the UK for sure, I would definitely choose Middlebury. The St Andrews economics programme could possibly get you a job in a bank, but so would similarly ranked UK schools like Exeter or Southampton. It is unlikely that St Andrews would give you any particular advantage, whereas Middlebury is a well funded and well regarded liberal arts college. UK fee status is definitely based on residency, and has nothing to do with owning property or paying tax in the UK. Regardless of your property, if you are not a resident of the UK, you are an overseas student. (Although until brexit presumably happens, EU residents can study in the UK at the EU rate.)
US colleges & universities are based on the Scottish system so not sure why you think that studying at St. Andrew’s would be “a new education system” to you.
For economics & geography majors, St. Andrews is the clear choice.
There is no geography or economics major at St Andrews. You apply to study geography or economics. There will be few to no electives and no general studies, although I have heard that claimed. Also, what evidence is there that US education is ‘based on the Scottish system’ . I would claim that it developed independently from general UK origins, but the broader emphasis in the nineteenth century ( compared to the UK) would typically be more German than Scottish.