I have one of each. By far, the RIR is friendlier - she will run down as soon as she sees me, is easy to put back in the coop when I need to and enjoys a cuddle. My Australorp is still very sweet, but just a little more "aloof". If I manage to catch her, she is still happy for a cuddle.
I got them at the same time and they were both point of lay. They have both been highly productive, regular egg layers. The RIR eggs are probably a little larger, but not by much. The RIR has been broody once over summer, the Australorp has not been broody yet (in about 15 months). They both free range very well.
My Australorp is probably 1.5 times the size of my RIR.
I think the Australorp is prettier, I love the green and purple gleam to her glossy black feathers.
I probably haven't helped at all, they are both nice (and cold tolerant - don't know if that helps). The RIR is probably a little easier (because of her friendly nature) to "control".