Any of the JP servers would be better for you (I'm Australian too and I play on a JP Legacy server), but Tonberry and Masamune have the biggest English-speaking populations so they'd be best for language reasons.

Incidentally, if you're having trouble finding a party in DF, one thing commonly overlooked is maybe set the DF to look for players with other languages (Japanese, French and German) - although communication might be difficult it's not impossible, and you'll be far more likely to get into a party that way rather than just looking for only English-speaking players.