hi guys
i'm going YYZ - SYD.
i have my choice of airlines to fly: AC, AA, CX, UA (goldpoints transfer to FF programs).
i'm wondering a couple things:
1. which would be the best? (in terms of service and access to lounges [for showers, alcohol, etc])
2. for UA, the difference between business class and first class is 20,000. is it worth it?
any help would be greatly appreciated

cheers
firefly