Hey Sunami,
Same as with surfing, the board has to match the conditions.
For waves 4-10 foot like if you are riding a wave like Margs mainbreak, then narrower and more pin tail for control and bottom turn at high speed. A flattish tail lift and less toe in on thruster fins. Basically more gun shapped. Control at speed is most critical.
For Perth slop in summer, you should be riding something with a wide tail, wide plan shape, short nose, lots of nose rocker, a little more tail rocker and nice and wide with soft rails. Hi speed control is not required. What is required is planing surface around the tail to give you as much drive and lift from the tiny wave faces and generally crumbly crap waves. Riding speed is generally lower so more toe in for the thrusters for control in tight grippy turns and slashes under the lip.
For an all rounder, waves from 2-5 foot, I'd go something similar to a normal surfboard with just a bit less tail lift and slightly harder rails a little further forward than a normal surfy. These boards wont work well in 1-2 foot Scarborough summer slop and wont handle big high speed bottom turns. It's always a compromise unless you ante up and have a board for each conditions.
I use three different boards. The '09 North Freestyle Fish 5'0" for Perth crap, The '09 Airush 6'0" Converse for 2-7 foot and the North Kontact 5'10" for 6'+
Just like surfing mate, no one board can do it all well.
Good waves,