The easiest way is most probably by train. All train starting in Bucharest's North Station(Gara de Nord) going in Moldova region(Iasi, Botosani, Suceava, Bicaz) go through Focsani.
The best trains are InterCity, they go fast, they are clean and confortable. But the Rapid train are quite good. A trip from Bucharest to Focsani takes aproximately 2 hours and 20 minutes.
Pictured is a DMU InterCity train.









