Why Flachau
Flachau is only 40 min's from Salzburg and 2 hours from Munich. The A10 from Salzburg is a motorway, so it's an easy drive to the apartment and snow tyres should be sufficient with no need for snow chains.
Budget flights are normally available to Salzburg and Munich all year round, so getting to Flachau is quick and easy.
Flachau is also at the centre of a large ski area of 350Km and a convenient base from which to visit other well known ski resorts. See skiing link above.