Sofia airport is to the east of the city and the route to Bansko is to the south west of the city. The driving in the capital is challenging and the traffic very bad during the rush hours. However transport into and around the town is good. The taxis are good value (check the Km cost on the window - top line day/night) and the trams fun! Remember to buy tickets for public transport at the kiosks before you get on and to stamp the tickets once on the bus or tram. The challenge is to know where the routes go; however, some of the many free maps have tram and/or bus routes marked.
Where to stay depends on your pocket and needs. From personal experience we can recommend the following:
3* Brod Hotel- excellently situated for an en-route overnight stay just off the ring road between the airport and the Bansko road. They will also do airport pick-ups, transfers and car rentals. This is our first choice of hotel as it avoids taking a car into the city centre. One has to take a taxi into the centre of the town but the cost is very low. Just remember to ask the hotel to write its name down in Cyrillic script to show the taxi driver!
3* Apartment House Dunav - a small hotel of apartments. Our family found the kitchen useful for meal preparation for their toddler.
We have also stayed at one or two less good hotels that seem to date from the communist period so take care when choosing.
There are a number of good websites that cover a high proportion of the hotels in Sofia and will offer a good deal. Try: