FAPP, 5.45 is the better round...
Between NATO, the ex-Pact, and now China, everyone major has or is leaving .30cal for a 5.xx mm round (5.45, 5.56, 5.8)... 7.62x39 will stay popular in the various backwater countries, but that's about it...
OTOH, 7.62x39 is cheaper...