Senior Trip: Japan or Australia?

[NeedsMoreNuts]

My parents' graduation gift to me is a trip to a place of my choice, and I've narrowed it down to two places: Japan and Australia. Both of my trips would be through a company with guides that take us to sights in the morning and and afternoon, and we would be free to go about on our own at night. At this point, either trip would be amazing to me, and I really can't decide between them.

Japan:
If I go to Japan, it would be for 9 days. We would stay in Osaka, Kyoto, and Tokyo. I would be going with a small group (around 15) of people from my school, along with my junior history teacher (he's only 28 and a cool guy).
Pros:
Japan, obviously
With a group of friends I already know and like
Everyone who has gone has said Japan is amazing
At 6'3, I'd be a giant
Cons:
Almost a week shorter than Australia
English is not official language (although I've heard that many younger people have a basic grasp)
Drinking age of 20 (I'll be 19 at the time of the trip)
It's not Australia and New Zealand

Australia:
I'd be in Australia and New Zealand for 15 days (something like 11 and 4 respectivly). It be with a group of around 25 18-30 year-olds that I've never met before (an outward bound style group). The general set up is the same: mornings and afternoons with a guide, evenings to ourselves.
Pros:
Australia and New Zealand, obviously
Almost a week longer than Japan
Meet new people
Drinking age is 18
Speak English
Cons:
Won't be going with any of my friends
Will be the baby of the group
It's not Japan

Now, everything I've written here under pros and cons are small things; nothing has really swayed me either way at this point. I'm really just looking for anyone who has been to either or both of the places. I'm equally happy exploring a big city or a hiking a national park. All help/advice is greatly appreciatted.