no matter which airport you fly into you will have access to public transport. Tegel has buses that run to Zoologischer Garten is a pretty major stop, and Schoenfeld has an SBahn that goes into Hauptbahnoff via an Airport Express...it's pretty tough to get lost so either way you will be fine.

Hopefully it is Tegel...it's the easiest airport to operate in (in the world) and you will be in Mitte from there with bus and subway in 45 minutes