From: Bristol, UK
It depends on your overall strategy to some degree.
This is what I'm doing in my current game where most of pz gr 2 has gone South so that supply towards Mogolev or Gomel is not needed.
FBD 4 Radviliskis Daugavpils, Pskov, Leningrad.
FBD 3 Kaunas, Vilnius, Daugavpils, Vitebsk, Smolensk, Vyasma.
FBD 2 Brest, Minsk, Smolensk, Bryansk, Orel.
FBD 1 Lvov, Tarnopol, Proskurov, Vinnitsa, Cherkassy, Poltava, Kharkov.
FBD 5 Kishinev, Odessa, Nikoleav, Zaporozhye, Stalino.
Note that doing it this way is not only efficient, but also the Northern 3 rail lines are linked at Daugavpils and Smolensk giving an early North-South connection.