The first decision in Mandurah is not which suburb — it is which water, and how far from the train. Everything else follows from that.
The three kinds of place
Canal and estuary. Halls Head, Erskine and Dudley Park put you on flat water, sometimes with a mooring at the door. This is the premium end, and the closest thing to the postcard, but you pay for the frontage.
The newer family estates. Madora Bay, Lakelands and Dawesville are where much of the growth — and the more affordable new housing — has gone: bigger blocks, newer schools, a longer run into the centre.
Central and the coast. Around the foreshore and the older beachside pockets you trade some space for walkability, the marina and the train.
The decision to make first
Rank three things in your own order: which water (and how close), value for space, and closeness to the Mandurah line if Perth is part of your plan. It is hard to have all three, and ranking them is what stops you renting or buying in the wrong half of the city.
Canal, coast or commuter belt — Mandurah is really three choices. Rank water, value and the train and the shortlist writes itself.