Hi mate,
i've lived in both cities in the past year. What is your focus on the trip exactly?

Perth and brisbane are probably the most two alike cities in australia in my opinion.

Perth is nice for its beaches, the swan river and Rottnest, the only place youwill find a 'quokka'.Perth weather is nice and warm in the summer but can get pretty stormy in the winter. Perth is the best place for a 'Sunday sesh' especially down at cottesloe. It's unique because you get to see the sun set over the coast whilst relaxing and having a drink. It's descirbed as a big small town city being so far away from everything else, the problem with that is the cost it takes to get back to the eastern states.

Brissie has awesome tropical-ish style weather and has a wicked location being that you can drive an hour or two north for the sunshine coast and noosa etc. or south for the gold coast and byron bay at the top of NSW. QLD does have all the theme parks if that is what you are looking for?

Hope that can help you a little bit. Let meknow if you want any more info