If I had a Sony I would use the US
Sony eBook Library (eBL) software and register as from the US no matter where I lived. This at a minimum gives you access to the Google public domain ePubs, and Sony's geographical restrictions now seem easier to work around than previously (although I am not sure of the details). This is probably the 2nd best single catalog in the US (after the Kindle Store), and therefore the best in ePub. I am not aware of any advantages to using the non-US software that comes with the device overseas - it does not include a built-in store and any Sony Reader can side-load ePubs from local retailers using the US eBL.