It really depends on your preference - some cafés will use a blend of 2 countries, but most recommend using a single origin bean (meaning the coffee grounds all come from one country.)
When choosing your coffee, think of the flavor profiles you like in coffee. Do you like your coffee to be earthy and nutty, with caramel notes? If so, you'll probably like a Central or South American coffee. One of my personal favorite countries for coffee is Colombia. However, if you like coffee that's bright, fruity, and floral with notes like berry, mango, and grape, you'll enjoy African coffee. Ethiopian coffee's a great bet!
When it comes to what type of roast, most would recommend a medium to medium-dark roast coffee.
To find great single origin coffee in your area, do some research on cafés and roasters local to you. You're sure to find something great. :)