GMT would be the least confusing thing. It's the one we're all used to calculating from.
In fact, as we become more global in our thinking I can't see why we wouldn't just have one time globally and it would be GMT.
Yes, downunder we'd start work in the morning at 0700 and get off at 1500 in the evening, and we'd have to drop words like noon, because high noon would be 10pm, but think of the ways companies and people would be able to interact with each other. We'd no longer be a day ahead all the time. If someone says phone me at 0800 on the 23rd, you'd know when that is.
Okay, maybe there are a few flaws in my reasoning...