There's really no best or worst uni for anything - something which is in the top ranks, has heaps of students, has a massive UAI cutoff (=high demand and/or low supply), etc may not be the best uni for you or your friend.
When I was looking at doing Japanese, I was personally looking to go to ANU and get involved in their year away program. Their degrees are really comprehensive, and the staff are great. Outside of ANU, most unis in Sydney have Japanese and are essentially as good as each other - you need to look at exchange/international options, and how they're funded.
Anyway, prepare yourself for students to come in and say "x uni is the best", simply because they go there.