It depends what you want, buying cars really is a personal choice. I can give you a few pros and cons though. Buying a used WRX to me spells trouble, its probably been thrashed and parts are not cheap, if anything breaks, they also consume alot of petrol when you drive them hard. If you did get a good one, it would be a nicer car to drive (I think) then a new holden. And I think resale value providing it is still in good shape when you sell it would be better then the new holden.
The new holden would probably be more fuel efficient and it comes with a warranty if anything goes wrong. But I think you would probably lose more value on resale.
If I was going to buy the WRX I would make sure a qualified mechanic checked it out first (one that works on WRX's regularly) and they gave you the go ahead.