Either one will be good, but you have to be aware of some things:
a) Most people prefer A380 over other aircraft, even in business (is it worth 2000 dollars though?) I love the A340-500/600's though.
b) Etihad's business class product is good, but it can be a bit cramped for taller/larger persons. The every other centre row is combined so it would be perfect to travel with your 2 year old
c) Etihad's ground service in Sydney is pretty terrible
d) The Etihad business class lounge in Abu Dhabi is often over crowded
e) You'll probably get a better meal service on Etihad