This was a fantastic trip. We flew Atlanta to Sofia (via CDG) on April 24 and returned from Bucharest (via AMS) on May 24.
For trip planning we used Brandt Guides - one titled Bulgaria and another titled Romania: Transylvania. We also used the Trip Advisor Forum and the suggestions of several here - thank you all!
Itinerary:
Sofia - 4 nights
Plovdiv - 4 nights
Veliko Tarnovo - 3 nights
Bucharest - 1 night
Sibiu - 4 nights
Cluj-Napoca - 3 nights
Sighișoara - 3 nights
Brasov - 4 nights
Bucharest - 3 nights
Transportation:
In Bulgaria, we traveled by bus/minivan between cities. In Romania, we took a train from Ruse to Bucharest and spent one night in Bucharest. We picked up a rental car at the Bucharest Airport.