Probably depends on what kind of fishing you do, and where.

 I fish around busselton bunbury area and hoping to do bottom bouncing in deeper water

better ride more stable only downside is they are heavier so if your going to tow them long distances you need a decent tow vehicle!

But you'll need a little more experience in choosing a good glass hull from an ali.

You'll have to do heaps of ground work on all the ins and outs. I believe its best to do it yourself and not rush into it.

My first boat was ali, nice and light easy to tow and beach launchable was the best thing. The glass boat has an amazing ride but heavy and thirstier. I had to buy new tow car just a added cost of glass. Just research and decide what you really want it for, some ali boats still have a half decent ride !!

for your budget, you would probably find the 4.5-5m ali's very common. There is nothing wrong with this. I've had fibreglass boats and found they are too heavy and not managable for me, so i prefer ali boats. If its your first boat, make sure you get something your comfortable with, and take into consideration things like launching and retrieving, towing etc. 

Something like this would get you to the 4 mile:

http://www.gumtree.com.au/s-ad/south-fremantle/boats-jet-skis/de-havilland-phantom-alum-runabout-4-65m-owner-moving-to-nsw/1004131980

i would say fibreglass, if you find the right boat and make you can get a great deal, my dad bought an older boat it was made by Guardian Industries and that a great smooth ride