score:3
This info is from May 2015.
It is possible to take a public bus from Medan's Pinang Baris bus station.
The price is of maximum 40'000 IDR per person.
The journey takes circa 3h45min.
You can take a tourist bus.
The price is of circa 100'000 idr per person.
The journey takes circa 3h.
Arrange the tourist bus directly with your hotel/guesthouse in Burkit Lawang or with a tourist agency (they call them "tourist information offices"!) in Burkit Lawang.
Public buses are usually small vans type legendary VW, with circa 12 seats but welcoming up to circa 16 people (or more?).
Tourist buses are usually quite modern Toyota car.
These are the pros & cons I can see, then it's just a matter of taste really.
Tourist bus pros: comfortable, aircon, no stops during journey, usually safer driving style, safer vehicle (they even have belts!), faster, may meet tourists giving you good tips
Tourist bus cons: only tourists inside
Public bus pros: travel like a local, pay less, mingle with the local, simply more fun
Public bus cons: a bit slower, reckless driving style, usually not very comfortable, no seat belts