Me personally well not to sound like a cold hearted dick cause I'm not but I just never heard about these at the time they happened. Of course though, both would have been awful I mean any terriost attack is bad and it disgusts me that people would do something like that.
The 9/11 well I was too young to understand back then.
The 7/7, I was obviously a bit older so I should have heard about it, didnnt hear about it though until this year and believe me I feel like a complete and utter Blue dumbass for never hearing of it espcially since it happened to a country closer to Australia than the 9/11. My fault, I never paid attention to news back then and my primary school never talked about it cause they were stupid. I pay more attention to things now though.
But for this country, I think the 7/7 affected Australia more, like Kizza said, it happened alot closer to our soil.