Renting a Car, Perth
Perth is one of those places where public transportation is for commuter traffic. Past peak hours, chances are, you are going to find it difficult to get around.
I would defintely rent a car. Cabs are expensive and hard to find and you'll have to call to get one.
Plus, having a car means that you can take off anywhere, north or south of the city for getaways to the South West where you will find wine country, karri forests and amazing coastlines -
Drive north where the landscape is remarkably different, coastline decidedly more rugged and where humble seaside resorts are.
Perth is a very modern city with excellent freeways and relatively quiet roads. You'll definitely want a car to get around.