Accurate satellite positioning on any of the systems depends on being able to "see" sufficient satellites (4+) to get a fix. With an open view of the horizon, any of the systems should get an accurate fix on its own, and accessing a 2nd system doesn't offer any advantage. Where you have an obscured view of the sky (eg. tall buildings, narrow valley), you increase your chances of being able to see 4+ satellites if you can access a 2nd constellation of satellites.
The Galileo fleet of satellites is not expected to achieve full operating capability until 2019. Glonass performance tends to be better at high latitudes than closer to the equator.
On this basis, I'd suggest GPS + Glonass for someone living in Sweden, but that may change next year.
