I've done this trip many times, generally through ORD. The only time I went through DEN I was headed to SYD and got caught in a snow storm in DEN and had to spend the night. Got a hotel room and some meal vouchers, but doesn't really compenstate for not being in SYD.

Generally I go with ORD because you receive more miles. 500 + 1,846 versus 8 something and 8 something. And given how unpredictable weather can be, I take the miles.