I have both... I'd hate to have to choose!... Blk Giants are "Giant" but I have an Aussie Roo that's a monster in his own right! I love em both a lot!
Just get both breeds!
Australorps are pretty, and the one hen I have is a sweetie who has a kind, gentle voice, but I gotta say I like the Jerseys better. As previously stated, they already come in more than one color, and they are majestic to look at (in my opinion)